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一、push() 和pop()
1.push()
push() 向数组的末尾添加一个或更多元素,并返回新的长度。
push源码如下:
// Appends the arguments to the end of the array and returns the new
// length of the array. See ECMA-262, section 15.4.4.7.
function ArrayPush() {
CHECK_OBJECT_COERCIBLE(this, "Array.prototype.push");
if (%IsObserved(this))
return ObservedArrayPush.apply(this, arguments);
var array = TO_OBJECT(this);
var n = TO_LENGTH_OR_UINT32(array.length);
var m = %_ArgumentsLength();
// It appears that there is no enforced, absolute limit on the number of
// arguments, but it would surely blow the stack to use 2**30 or more.
// To avoid integer overflow, do the comparison to the max safe integer
// after subtracting 2**30 from both sides. (2**31 would seem like a
// natural value, but it is negative in JS, and 2**32 is 1.)
if (m > (1 << 30) || (n - (1 << 30)) + m > kMaxSafeInteger - (1 << 30)) {
throw MakeTypeError(kPushPastSafeLength, m, n);
}
for (var i = 0; i < m; i++) {
array[i+n] = %_Arguments(i);
}
var new_length = n + m;
array.length = new_length;
return new_length;
}
这是v8的源码地址 第538行
这里的代码比较简单,从源码中可以看出用法:
方法中可以传多个参数,参数长度不超过2的30次方
var arr = [1,2];
arr.push(3); //arr--->[1,2,3] return 3;
arr.push(4,5);//arr--->[1,2,3,4,5] return 5;
1.pop()
删除数组的最后一个元素,并返回新的长度。
// Removes the last element from the array and returns it. See
// ECMA-262, section 15.4.4.6.
function ArrayPop() {
CHECK_OBJECT_COERCIBLE(this, "Array.prototype.pop");
var array = TO_OBJECT(this);
var n = TO_LENGTH_OR_UINT32(array.length);
if (n == 0) {
array.length = n;
return;
}
if (%IsObserved(array))
return ObservedArrayPop.call(array, n);
n--;
var value = array[n];
%DeleteProperty_Strict(array, n);
array.length = n;
return value;
}
这是v8的源码地址 第497行
如果arr长度为0,返回undefined
var arr = [1,2];
arr.pop(); //arr--->[1] return 1
arr.pop(); //arr---->[] return 0;
arr.pop(); //arr---->[] return undefined
push(),pop()功能是通用的; 它不要求它的这个值是一个Array对象。因此,它可以转移到其他类型的对象以用作方法。函数是否可以成功应用于宿主对象取决于实现。
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