Why use === instead of == when comparing a String

This question already has an answer here:

Which equals operator (== vs ===) should be used in JavaScript comparisons? 50 answers

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The === operator ensures that not only the values are equal, but the two items being compared are of the same type too; Whereas the == operator only checks that the values of the two items are equal

As @amnotiam mentioned in the comments, you may also want to check out the The Abstract Equality Comparison Algorithm

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=== is used for checking value with type..

var str="300";

//this gt execute
if(str==="300")
{
        alert("this alert get executed");
}


//this not execute
if(str===300)
{
        alert("this alert not get executed");    
}

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for == below both code is valid because its not check for type

//this get execute
if(str=="300")
{
        alert("this alert get executed");
}


//this get execute
if(str==300)
{
        alert("this alert get executed");
}

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10 == '10'  // true  | check value: 10 equal 10
10 == 10    // true  | check value: 10 equal 10

10 === '10' // false | check type: int not equal string
10 === 10   // true  | check type: int equal int, check value: 10 equal 10

检查类型与否。

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