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JS Learner Forms — First Form

The Explanation

You can also look at JS Learner Forms documentation for other forms.

You will be working in then jsforms-source/1_first-form.js file.

Table Of Contents

Variables and Operations

You will explore the creation and use of variables.

declaration and initialization

Here you will declare and initialize variables.

It should have a variable called "a"

Create a variable at the top of the block called "a". You will need to use let or var.

Hints

Be sure you use "var" or "let" to declare your variable

Code

Example 1

const jsforms = (function () {
    'use strict';
    let ?;

    return {
    };
})();

Example 2

const jsforms = (function () {
    'use strict';
    var ?;

    return {
    };
})();

It should initialize "a" with the value 5

Set the initial value of a to 5.

Hints

Initialize a variable with equals: var a = ...

Code

Example 1

const jsforms = (function () {
    'use strict';
    let a = ?;

    return {
    };
})();

Example 2

const jsforms = (function () {
    'use strict';
    var a = ?;

    return {
    };
})();

assignment and operators

Now that you have a variable you will assign it a value different then what it was initialized with.

It should assign the sum of 3 and 7 (3 + 7) to "a"

Now assign variable a with the value of 3 + 7.

Hints

Add two numbers using the plus (+) operator

Code

Example 1

    let a = 5;
    a = ? + ?;

    return {
    };

Example 2

    var a = 5;
    a = ? + ?;

    return {
    };

It should have a variable "b" initialized to "Hello, World!"

Create a variable called b and initialize it with the value `"Hello, World!"

Hints

Initialize a variable with equals: var b = ...

Code

Example 1

    let b = ?;

    return {
    };

Example 2

    var b = ?;

    return {
    };

method call

YOu will make a call to a method on an object.

It should log variable "b" to the console

Use the console.log method to log the value contained in variable b to the console.

Hints

Console.log might be just the ticket...

Code

Example 1

    console.log(?);

    return {
    };

Example 2

    console.log(?);

    return {
    };

exposing values

You well now expose values to the outside world.

It should expose variable "b" to be read outside of the module

Expose the variable b to the outside world, by adding it the the object being exported.

Hints

Find return {}; add a "b" -> return {b};

Code

Example

    return {
        ?,
    };

Function Creation

[function declaration, return statement]

Time to create functions and have them return a value.

**greeter function**

It should say "Hello!" by default

Write a function called greet that returns the value "Hello!". (note: don't forget the "!")

Hints

Functions start with the keyword function followed by the name of the function and then a set of parenthesis (). All the logic of a function is contained an open curly brace { and a closed curly brace }. What the function returns follows the key word return.

Code

Example

    function greet() {
        return _string_;
    }

    return {
        greet,
    };

conditional logic [if/else]

It should say "Salutations!" when Salutations is passed

Modify the greet function to take a greeting and return the greeting if it was passed.

Hints

Add condition to greet to handle custom greeting case. (Try using an "if/else" structure. "If" is a control structure)

Code

Example

    function greet (greeting) {
        if (_something_ === undefined) {
            return _string_;
        } else {
            return _something_ + '!';
        }
    }

    return {
        greet,
    };

function calls and mathematical operations [Math library]

**square function**

Create a function that takes a number and returns its square.

It should square 1

The function called square will be passed 1 and should return 1.

Hints

Add square function that returns a simple value rather then worrying about actually squaring the a value.

Code

Example

    function square(_something_) {
        return ?;
    }

    return {
        square,
    };
It should square 3

Modify the square function such that it returns the square of the value passed in.

Hints
  1. Add logic to correctly square a number (remember n^2 <=> n * n)
  2. Move to library function to perform square operation
    1. Math is a built in library...
Code

Example 1

    function square(_something_) {
        return ? * ?;
    }

    return {
        square,
    };

Example 2

    function square(_something_) {
        return Math.pow(?, 2);
    }

    return {
        square,
    };

**squareRoot function**

Create a function that takes a number and returns the square root of that number. (note: use the Math library).

It should take the square root of 1

Create a function called squareRoot that will be passed 1 and return 1.

Hints

Create a function that returns a simple value rather then worrying about actually performing a square root of the value.

Code

Example

    function squareRoot(_something_) {
        return ?;
    }

    return {
        squareRoot,
    };
It should take the square root of 4

Modify the squareRoot function to return the square root of the value passed.

Hints

Add logic to properly take square root (There is more than one way to solve this in one line, maybe with Math)

Code

Example

    function squareRoot(_something_) {
        return Math.sqrt(_something_);
    }

    return {
        squareRoot,
    };

Arrays, Loops, and Function Calls

You will use functions to work with arrays and loops.

**sum function**

You are going to create a function called sum that adds numbers together.

It should take the sum of one number

Create a sum function that accepts an array and returns 1.

Hints

Create a function that returns a simple number instead of worrying about actually adding numbers together.

Code

Example

    function sum(_something_) {
        return ?;
    }

    return {
        sum,
    };

It should add two numbers

Modify the sum function so that it adds the first two numbers in an array.

Hints

Add logic to sum 1 or two numbers (An if structure might help here)

Code

Example

    function sum(_array_) {
        if(_array_.length === 1) {
            return _array_[0];
        } else {
            return _array_[0] + _array_[1];
        }
    }

    return {
        sum,
    };

It should add multiple numbers

Modify the sum function to add all numbers in an array.

Hints

Add logic to sum an arbitrary length array of numbers (A for loop might help to accomplish this loops, like ifs, are control structures)

Code

Example 1 (let)

    function sum(_array_) {
        let result = ?;

        for(let index = _number_; _number_ < _number_; index += 1) {
            result += _something_;
        }

        return result;
    }

    return {
        sum,
    };

Example 2 (var)

    function sum(_array_) {
        var result = ?;

        for(let index = _number_; _number_ < _number_; index += 1) {
            result += _something_;
        }

        return result;
    }

    return {
        sum,
    };

**squareAll function**

Create a function that squares each number in an array.

The steps you will take to building the squareAll function are:

  1. Add a squareAll function that returns a constant value.
  2. Chang the squareAll function to perform square computation on array value

It should square all numbers in a single-value array

Create a function called squareAll that takes an array and returns the square of the first element.

Hints

Create a function that only squares the first value of an array and returns that value as an array.

Code

Example

    function squareAll (values) {
        let result = square(_array_[_number_]);
        return [_something_];
    }

    return {
        squareAll,
    };

It should square multiple numbers

Modify the squareAll function so that it now squares each number in the array.

Hints

Add logic to square all numbers in array (How did you solve sum?)

Code

Example

    function squareAll (values) {
        for(let index = _number_; _number_ < _number_; index += 1) {
            result[index] = square(_something_[index]);
        }

        return ?;
    }

    return {
        squareAll,
    };

Combining Complex Functions

You will use previous functions chained to gether to give us new results.

**sumOfSquares function**

Create a function that takes an array of numbers, squares each number and then returns the sum of those squares.

It should square number in a 1-length array and return it

Create a function called sumOfSquares that takes an array and returns the square of the first element.

Hints

Try to do the following:

  1. Add function sumOfSquares that returns the first element of the parameter
  2. Then add logic to square a single number inside the sumOfSquares function
Code

Example

    function sumOfSquares(_something_) {
        return square(?[0]);
    }

    return {
        sumOfSquares,
    };

It should take the sum of squares of multiple numbers

Modify the sumOfSquares function so that it squares all numbers in the array.

Hints

Add logic to square all numbers and return the sum (squareAll and sum might be useful to accomplish this)

Code

Example

    function sumOfSquares(_something_) {
        return add(squareAll(?));
    }

    return {
        sumOfSquares,
    };

Copying Arrays

Using Array.slice

You are going to use functions to explore the Array.prototype.slice method.

**buildVector function**

You will now create a function called buildVector that returns a copy of the array as it was passed.

A vector is an ordered set of points which describes a "directed line segment," in other words, a vector is a line segment with an arrow

It returns a vector (array) containing the same numbers as the original -- try returning the array you get in your function

Create a function called buildVector that returns the same array passed to it.

Hints

Add buildVector function (Would it be possible to just return something?)

Code

Hint

    function buildVector (values) {
        return ?;
    }

    return {
        buildVector,
    };

It returns a copy of the original vector

Modify the buildVector function so that it returns a copy of the array passed to it. (note: use the slice method on array.)

Hints

Add logic to return a copy of vector array (Slice will create a new array just like the old one...)

Code

Hint

    function buildVector (values) {
        let vector = _array_.slice(_number_);
        return vector;
    }

    return {
        buildVector,
    };

Combining existing code to solve new problems

You will now take code you wrote and use it define more complex behaviors

**magnitude function**

You will create a function called magnitude that will calculate the magnitude of all given numbers.

A magnitude is the length of a vector. You will explore computing the magnitude in the following tests

The magnitude of a vector is computed by:

  1. Square all numbers in the array
  2. Add all squared values together
  3. Take the square root of the sum of squares

such that given:

a = 1 b = 2 c = 2

the magnitude is:

√d = √(a² + b² + c²)

or

√d = √(1² + 2² + 2²)

√d = √(1 + 4 + 4)

√d = √9

d = 3

It returns the magnitude of a vector with only one number

Create a function called magnitude that returns the first item in an array that is given to it.

Hints

Can you just return a value from the array?

Code

Example

    function magnitude(_something_) {
        return ?[0];
    }

    return {
        magnitude,
    };

It returns only positive numbers -- all magnitudes are positive

Modify the magnitude function that returns the positive value of the first item in an array that is given to it.

Hints

Add logic to ensure magnitude is always positive (Hint: squaring a negative number makes it positive)

A magnitude is the length of a vector. you will explore computing the magnitude in the following tests.

Currently the magnitude of a vector is computed by:

  1. Square first value in the array
  2. Take the square root of the sum of that value
Code

Example

    function magnitude(_something_) {
        return squareRoot(square(?[0]));
    }

    return {
        magnitude,
    };

It should return the magnitude of a vector with two values

Modify the magnitude function so that it returns the magnitude of the first 2 items in an array given to it.

Hints

Add logic to perform proper magnitude calculation for length 1 and 2 vectors (A length 2 vector's magnitude can be computed by squareRoot(vector[0]^2 + vector[1]^2))

A magnitude is the length of a vector. You will explore computing the magnitude in the following tests.

Currently the magnitude of a vector is computed by:

  1. Square the fist 2 values of the array
  2. Add those values together
  3. Take the square root of the sum of those values
Code

Example

    function magnitude(_something_) {
        if (?.length === 2){
            return squareRoot(square(?[0]) + square(?[1]));
        } else {
            return squareRoot(square(?[0]));
        }
    }

    return {
        magnitude,
    };

It should return the magnitude of a vector with multiple values

Modify the magnitude function so that it returns the magnitude of all the values in the array.

Hints

Add logic to compute the magnitude of an arbitrary length vector. (The general magnitude formula is the square root of the sum of the squares. Can you apply functions you have already created?)

A magnitude is the length of a vector. You will explore computing the magnitude in the following tests.

The magnitude of a vector is computed by:

  1. Square all numbers in the array
  2. Add all squared values together
  3. Take the square root of the sum of squares
Code

Example

    function magnitude(_something_) {
        return squareRoot(sumOfSquares(?));
    }

    return {
        magnitude,
    };

Looping and inequality comparison

Now it is time to use functions to examine looping and comparisons.

**getVectorsShorterThan**

You will now create a function called getVectorsShorterThan that will take an array of arrays. It will compare each array based on its magnitude and return all arrays that have a magnitude smaller then the number provided.

the signature will be:

getVectorsShorterThan(length, arrayOfVectors)

Such that length is the number for which You will compare magnitudes against, and arrayOfVectors is the array of arrays, where then inner arrays are to contain numbers.

It returns an array of one vector when the vector is shorter than 5 -- arguments are: length, arrayOfVectors

Create a the function getVectorsShorterThan where the first parameter is length and the second parameter is arrayOfVectors that returns all vectors where the magnitude is less then 5. There is only one vector at this point and its length is less then 5.

Hints

Can you just return the first value of the array?

Code

Example

    function getVectorsShorterThan(length, arrayOfVectors) {
        return [?[0]];
    }

    return {
        getVectorsShorterThan,
    };

It returns an empty array when all vectors are too long -- tests one vector

Modify the getVectorsShorterThan function so that it will return an empty array if the first vector has a magnitude longer then length.

Hints

Add logic to handle the case where a vector is too long (How might you compare the magnitude of a vector to a length value?)

Code

Example 1 (let)

    function getVectorsShorterThan(length, arrayOfVectors) {
        let firstMagnitude = magnitude(?[0]);

        if (length <= firstMagnitude) {
            return ?;
        }

        return [?[0]];
    }

    return {
        getVectorsShorterThan,
    };

Example 2 (var)

    function getVectorsShorterThan(length, arrayOfVectors) {
        var firstMagnitude = magnitude(?[0]);

        if (length <= firstMagnitude) {
            return ?;
        }

        return [?[0]];
    }

    return {
        getVectorsShorterThan,
    };

It returns an array of more than one vector when all are short enough

Modify the getVectorsShorterThan function so that it returns all vectors if the first one has a magnitude less then the length.

Hints

Add logic to handle 0, 1 or 2 vector cases

Code

Example 1 (let)

    function getVectorsShorterThan(length, arrayOfVectors) {
        let firstMagnitude = magnitude(?[0]);

        if (length <= firstMagnitude) {
            return [];
        }

        return ?;
    }

    return {
        getVectorsShorterThan,
    };

Example 2 (var)

    function getVectorsShorterThan(length, arrayOfVectors) {
        var firstMagnitude = magnitude(?[0]);

        if (length <= firstMagnitude) {
            return [];
        }

        return ?;
    }

    return {
        getVectorsShorterThan,
    };

It returns only vectors which are not too long

Modify the getVectorsShorterThan function so that it now returns only those vectors with a magnitude less then the length.

Hints

Move to general code for filtering vecctors (Is there a way you can use a known control structure to check all vectors?)

Code

Example 1 (let)

    function getVectorsShorterThan(length, arrayOfVectors) {
        let result = ?;

        for(let index = _number_; _number_ < _number_; index += 1) {
            let currentMagnitude = magnitude(?[index]);
            if (currentMagnitude < length) {
                result.push(buildVector(?[0]));
            }
        }

        return result;
    }

    return {
        getVectorsShorterThan,
    };

Example 2 (var)

   function getVectorsShorterThan(length, arrayOfVectors) {
        var result = ?;

        for(let index = _number_; _number_ < _number_; index += 1) {
            let currentMagnitude = magnitude(?[index]);
            if (currentMagnitude < length) {
                result.push(buildVector(?[0]));
            }
        }

        return result;
    }

    return {
        getVectorsShorterThan,
    };

The Other JS Learner Forms

JS Learner Forms documentation