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JavaScript Equality Operators

flaviocopes profile image flavio ⚑️πŸ”₯ Originally published at flaviocopes.com on ・1 min read

Those operators accept two values and return a boolean:

  • == checks for equality
  • != checks for inequality
  • === checks for strict equality
  • !== checks for strict inequality

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.

Examples:

const a = true

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

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

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

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

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

Discussion

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webdeasy profile image
WebDEasy

How did you "Originally published at" in the post title? :o

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flaviocopes profile image
flavio ⚑️πŸ”₯ Author

I think dev.to does it automatically when you set the canonical meta tag!

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dance2die profile image
Sung M. Kim

As @flavio said it's the "canonical url" that does the job.

For more info, check out "Front Matter -> canonical_url" in the Editor Guide.

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novajay2415 profile image
NovaJay2415

That's really interesting! Thank you for pointing that out. It will definitely help me out... Just starting to learn JavaScript.