JavaScript Equality Operators

Those operators accept two values and return a boolean:

• == checks for equality

• != checks for inequality

• === checks for strict equality

• !== checks for strict inequality

inv

Let’s talk what we mean for strict. Without the strict check, the second operand is converted to the type of the first before making the comparison. Strict prevents this.

inv

Examples:

const a = true

a == true  // true
a === true // true

1 == 1     // true
1 == '1'   // true
1 === 1    // true
1 === '1'  // false

inv

You cannot check objects for equality: two objects are never equal to each other. The only case when a check might be true is if two variables reference the same object.

Some peculiarities to be aware: NaN is always different from NaN.

NaN == NaN // false

inv

null and undefined values are equal if compared in non-strict mode:

null == undefined  // true
null === undefined // false

inv

Example:

false == '0'  // true
false === '0' // false

true — double equal performs a type conversion

false — triple equal is more strict and does no type conversion becouse both type and value have to be the same

Really important to know the difference with JS 👌

inv

Things to Remember

✦ The == operator applies a confusing set of implicit coercions when its arguments are of different types.

✦ Use === to make it clear to your readers that your comparison does not involve any implicit coercions.

✦ Use your own explicit coercions when comparing values of different types to make your program’s behavior clearer.

inv

[ ECMAScript 6: ] The Object.is() Method

In many cases, Object.is() works the same as the === operator. The only differences are that +0 and -0 are considered not equivalent and NaN is considered equivalent to NaN. But there’s no need to stop using equality operators altogether.

Choose whether to use Object.is() instead of == OR === based on how those special cases affect your code.

inv

The Legend of JavaScript Equality Operator

inv

inv inv

JavaScript Equality Operators

Examples:

Example:

Things to Remember

[ ECMAScript 6: ] The Object.is() Method

HappySoloLearning ;) by @booleanmaybe