what does the !== operator do in javascript?

Question

if (description !== undefined)

i found this in nerd dinner tutorial.

Related question: http://stackoverflow.com/questions/359494/javascript-vs-does-it-matter-which-equal-operator-i-use — Drazar, Jan 28 '11 at 07:58

score 4 · Answer 1 · answered Jan 28 '11 at 07:57

It is identity operator that not only checks for value but also type.

Example:

if (4 === 4)  // both type and value are same
{
  // true
}

but

if (4 == "4")  // value is same but type is different but == used
{
  // true
}

and

if (4 === "4")  // value is same but type is different but === used
{
  // false
}

You should use === or !== once you are sure about both value and type.

score 2 · Accepted Answer · edited Jan 28 '11 at 08:11

2

This is the strict not equal operator and only returns a value of true if both the operands are not equal and/or not of the same type. The following examples return a Boolean true:

a !== b 
a !== "2" 
4 !== '4'

For more operator information refer here Dev Guru Forum

edited Jan 28 '11 at 08:11

aaronasterling

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answered Jan 28 '11 at 07:58

Subhash Dike

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score 1 · Answer 3 · answered Jan 28 '11 at 07:58

1

This is the strict not equal operator and only returns a value of true if both the operands are not equal and/or not of the same type.

answered Jan 28 '11 at 07:58

Fredrik Widerberg

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what does the !== operator do in javascript?

3 Answers3