Iterate Array Avoid Using for…in 和 for…of
Iterate 陣列時避免使用for…in, for…of 因可能有非預期的值出現。
Example
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| var a = []; // Create a new empty array.
a[5] = 5; // Perfectly legal JavaScript that resizes the array.
for (var i = 0; i < a.length; i++) {
// Iterate over numeric indexes from 0 to 5, as everyone expects.
console.log(a[i]);
}
/* Will display:
undefined
undefined
undefined
undefined
undefined
5
*/
--------
var a = [];
a[5] = 5;
for (var x in a) {
// Shows only the explicitly set index of "5", and ignores 0-4
console.log(x);
}
/* Will display:
5
*/
上述用同一個Example不同for方法~兩個例子會有不同的結果，且for...in是非預期的。
因此避免使用
|