Javascript Eval覆盖变量 [英] Javascript Eval overwriting variable

问题描述

不明白为什么下面的代码会覆盖我的var arr.任何帮助表示赞赏.

Don't understand why the code below is overwriting my var arr. Any help appreciated.

var arr = [1,2,3]

var string = "function swap(arr) { var newarr = arr; var temp = arr[0]; newarr[0] = arr[arr.length-1]; newarr[arr.length-1] = temp; return newarr }"

var test = eval("[" + string + "]")[0];

test(arr);
console.log(arr);
//this outputs [3,2,1]

test(arr);
console.log(arr);
//this outputs [1,2,3]

小提琴

谢谢

推荐答案

由于在JavaScript中，对象是通过引用值传递的，而数组是对象.评估在这里无关紧要.这是在没有eval的情况下产生相同问题的代码:

Because in JavaScript, objects are pass by reference value and arrays are objects. The eval is irrelevant here. Here is code producing the same issue without eval:

var arr = [1,2,3];
var arr2 = arr; // this just sets the reference
arr2[1] = 3; // this also changes arr
arr[0] = 3; // this also changes arr2
arr; // [3, 3, 3]
arr2; // [3, 3, 3]

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