If I create a 2D Array in JavaScript and try to assign one specific object it changes all. Here is my Code:
var a = [0,1];
var b = [];
b.push(a);
b.push(a);
b[0][0]=5;
alert(b[1][0]);
Now I expect to get 0 but I get 5. How can I fix this?
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3 Answers
You push the same object reference. by chaging one value, all references shows the changed value. Instead, you could spush a copy of the array by taking Array#slice.
var a = [0, 1];
var b = [];
b.push(a.slice());
b.push(a.slice());
b[0][0] = 5;
console.log(b[1][0]);
console.log(b);
Comments
you're pushing array which is reference so value at both the index refer to a ( reference to a ) which is why change at any index will reflect on all the other indexes which points to same reference, you need to add value you can see i am using spread syntax for creating a copy of array
b.push([...a]);
var a = [0,1];
var b = [];
b.push(a);
b.push([...a]);
b[0][0]=5;
console.log(b);
Comments
By calling b.push(a) twice you are assigning the same array a to the first and second index of b. Therefore if you edit elements of a then it will be reflected for all references of the same instance.
You can perform a deep copy of a to prevent this.
E.g.,
b.push(a.slice());
b.push(a.slice());
