# JavaScript Equality Algorithms

(Loose) implementation of the double equals (==) and triple equals (===) algorithms in JavaScript, showing the steps the JavaScript engine takes to evaluate both operations and how the operations are related.

## Algorithms

The algorithms are in the /code/algorithms folder of this repo. If you want to have a quick look, here's a Gist with algorithm implementations

### ==

Implementation based on the Spec

``````function doubleEquals(x, y) {

// if x and y have the same type
if (areSameType(x, y)) {
// return the === comparison (based on the spec, this should run the code from step 2 of the === algorithm but this is a cleaner representation)
return tripleEquals(x, y);
}
// x and y have a different type
else {

// if x is null and y is undefined,
// return true
if (isNull(x) && isUndefined(y)) {
return true;
}

// if x is undefined and y is null,
// return true
if (isUndefined(x) && isNull(y)) {
return true;
}

// if x is a number and y is a string
// return the comparison x == toNumber(y)
if (isNumber(x) && isString(y)) {
return doubleEquals(x, toNumber(y));
}

// if x is a string and y is a number
// return the comparison toNumber(x) == y
if (isString(x) && isNumber(y)) {
return doubleEquals(toNumber(x), y);
}

// if x is a boolean,
// return the result of the comparison toNumber(x) == y
if (isBoolean(x)) {
return doubleEquals(toNumber(x), y);
}

// if y is a boolean
// return the result of the comparison x == toNumber(y)
if (isBoolean(y)) {
return doubleEquals(x, toNumber(y));
}

// if x is either a string or a number and y is an object
// return the result of comparison x == toPrimitive(y)
if (isStringOrNumber(x) && isObject(y)) {
return doubleEquals(x, toPrimitive(y));
}

// if x is an object and y is either a string or a number
// return the result of the comparison toPrimitive(x) == y
if (isObject(x) && isStringOrNumber(y)) {
return doubleEquals(toPrimitive(x), y);
}
}

//return false
return false;
}``````

### ===

Implementation based on the Spec

``````function tripleEquals(x, y) {
if (!areSameType(x, y)) {
return false;
}

// if both are undefined,
// return true
if (isUndefined(x)) {
return true;
}

// if both are null,
// return true
if (isNull(x)) {
return true;
}

// if both are numbers
if (isNumber(x)) {

// if x is NaN,
// return false
if (isNaN(x)) {
return false;
}

// if y is NaN,
// return false
if (isNaN(y)) {
return false;
}

// if both have equal Number values,
// return true
if (areEqualNumberValues(x, y)) {
return true;
}

// if x is a positive zero and y is a negative zero,
// return true
if (isPositiveZero(x) && isNegativeZero(y)) {
return true;
}

// if x is a negative zero and y is a positive zero,
// return true
if (isNegativeZero(x) && isPositiveZero(y)) {
return true;
}

// otherwise return false
return false;
}

// if both are strings
if (isString(x)) {

// if both are the exactly same sequence of characters
// (same length and same characters in corresponding positions),
// return true
if (areAllCharsEqualInOrder(x, y)) {
return true;
}

// otherwise return false
return false;
}

// if both are booleans
if (isBoolean(x)) {

// if both are true or both are false,
// return true
if (areBothTrue(x, y) || areBothFalse(x, y)) {
return true;
}

// otherwise return false
return false;
}

// if both refer to the same object,
// return true
if (areEqualReferences(x, y)) {
return true;
}

// otherwise return false
return false;
}``````

# JS Equality Algorithms

## Demonstration of the == and === algorithms in JavaScript

### JS Equality Algorithms Info

⭐ Stars 17
🔗 Homepage nem035.github.io
🔗 Source Code github.com
🕒 Last Update 9 months ago
🕒 Created 6 years ago
🐞 Open Issues 0
➗ Star-Issue Ratio Infinity
😎 Author nem035