What is the function of !!() in js? Detailed explanation of the role of !!() in js

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We know that JavaScript is a weakly typed language, but sometimes it needs to be forced to the corresponding type during use. so,! ! (), this writing method has the effect of converting weak types into strong types.

When it comes to type conversion, we have to mention two concepts: explicit conversion and implicit conversion.

Explicit conversion:

const a = parseInt（‘1111111111111’）；
const b = Obj.toString（）；

Implicit conversion:

var a = '111'+0;//a的结果为数值型；
var b = 111+'';//b的结果为字符串类型；

Return to !!().

For example: a defaults to undefined! a is true! ! a is false, so the value of b is false, not undefined. Writing this way can facilitate subsequent judgment and use.

so,! ! The function of (a) is to cast a to boolean.

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