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javascript double exclamation mark

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Adventurous Ape answered on February 27, 2021 Popularity 10/10 Helpfulness 1/10

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-2

console.log(!!navigator.userAgent.match(/MSIE 8.0/));  
// returns either true or false

Popularity 10/10 Helpfulness 1/10 Language javascript

Source: stackoverflow.com

Tags: double javascript

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Contributed on Apr 08 2021

Adventurous Ape

0 Answers Avg Quality 2/10

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js double exclamation mark

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// "!!" converts a value to a boolean, then inverts it and then inverts it again.
// So let's say you want to check the value for a given variable:
!!false // false
!!true // true

!!0 // false
!!parseInt("foo") // false — NaN is falsy
!!1 // true
!!-1 // true  — negative number is truthy
!!(1/0) // true  — Infinity is truthy

!!"" // false — empty string is falsy
!!"foo" // true  — non-empty string is truthy
!!"false" // true  — ...even if it contains a falsy value

!!window.foo // false — undefined value is falsy
!!undefined // false — undefined primitive is falsy
!!null // false — null is falsy

!!{} // true  — an (empty) object is truthy
!![] // true  — an (empty) array is truthy

Popularity 9/10 Helpfulness 7/10 Language javascript

Source: stackoverflow.com

Tags: double do

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Contributed on Feb 19 2024

Smart Morty

0 Answers Avg Quality 2/10

js double exclamation mark

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// "!!" converts a value to a boolean, then inverts it and then inverts it again.
// So let's say you want to check the value for a given variable:
const num = null; 

if (num) { // false -> value is null -> evaluated as falsy
}
if (!num) { // true
}
if (!!num) { // false
}
// another example
const str = "Hello World";

if (str) { // true -> value is a "proper" (not empty) string -> evaluated as truthy
}
if (!str) { // false
}
if (!!str) { // true
}

Popularity 10/10 Helpfulness 4/10 Language javascript

Source: Grepper

Tags: double do

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Contributed on Dec 22 2021

Pl0erre

0 Answers Avg Quality 2/10

double exclamation mark js

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// Converts anything to boolean. 

!!false === false
!!true === true

!!0 === false
!!1 === true

!!parseInt("foo") === false // NaN is falsy
!!-1 === true               // -1 is truthy
!!(1/0) === true            // Infinity is truthy

!!"" === false              // empty string is falsy
!!"foo" === true            // non-empty string is truthy
!!"false" === true          // ...even if it contains a falsy value

!!window.foo === false      // undefined is falsy
!!null === false            // null is falsy

!!{} === true               // an (empty) object is truthy
!![] === true               // an (empty) array is truthy; PHP programmers beware!

Popularity 10/10 Helpfulness 2/10 Language javascript

Source: stackoverflow.com

Tags: double do

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Contributed on Feb 27 2021

Molestable Carrot

0 Answers Avg Quality 2/10

javascript double exclamation mark

Comment

-2

const isIE8 = !! navigator.userAgent.match(/MSIE 8.0/);  
console.log(isIE8); // returns true or false

Popularity 10/10 Helpfulness 1/10 Language javascript

Source: stackoverflow.com

Tags: double do

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Contributed on Apr 08 2021

Adventurous Ape

0 Answers Avg Quality 2/10

javascript double exclamation mark

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