CODEWITHSUNDEEP
javascriptnode.js
NoDirection
NoDirection

Reputation: 122

javascirpt could not found when use bind

I had two arrays for storing function/method. when I did not use bind , I could find the index in the array. but when I used bind , it could not be found.

   function print(){}

    var functionArray1 = new Array();
    functionArray1.push(print);
    console.log(functionArray1.indexOf(print));

    var functionArray2 = new Array();
    functionArray2.push(print.bind(this));
    console.log(functionArray2.indexOf(print.bind(this)));

result: 0 -1

Upvotes: 2

Views: 86

Answers (2)

jonathangersam
jonathangersam

Reputation: 1147

when I used bind , it could not be found

Every time you use .bind(), it returns a new function. Since you called it twice, 2 new functions got created, and one isn't the same as the other (they point to different memory addresses).

function print() {}

const printA = print.bind(this) // this generates a function at a certain memory address
const printB = print.bind(this) // this generates another function at another memory address

console.log("is printA == printB ?", printA == printB) // false

const printC = printA          // this declares a new constant that points to an existing address
console.log("is printC == printA ?", printC == printA) // true

Hope this helps clarify. Cheers,

Upvotes: 0

CertainPerformance
CertainPerformance

Reputation: 371029

bind creates a new function. indexOf will only return zero or a positive index if the passed object exactly matches one of the items in the array - so, for example, for objects, functions, and primitives, they must be === for the indexOf test to pass.

function print() {}
const boundPrint = print.bind(this);
console.log(boundPrint === print);

Otherwise, if the passed object is not === to any elements in the array, -1 will be returned by indexOf. This is expected behavior.

Upvotes: 1

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