ES6中新添加的Array.prototype.fill

用法

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array.fill(start=0, end=this.length)

示例

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[1, 2, 3].fill(4)            // [4, 4, 4]

[1, 2, 3].fill(4, 1)         // [1, 4, 4]

[1, 2, 3].fill(4, 1, 2)      // [1, 4, 3]

[1, 2, 3].fill(4, 1, 1)      // [1, 2, 3]

[1, 2, 3].fill(4, -3, -2)    // [4, 2, 3]

[1, 2, 3].fill(4, NaN, NaN)  // [4, 4, 4]

[].fill.call({length: 3}, 4) // {0: 4, 1: 4, 2: 4, length: 3}

向前兼容方案

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if (![].fill) {

  Array.prototype.fill = function(value) {

 

    // Steps 1-2.

    var O = Object(this);

 

    // Steps 3-5.

    var len = parseInt(O.length);

 

    // Steps 6-7.

    var relativeStart = parseInt(arguments[1] || 0);

 

    // Step 8.

    var k = relativeStart < 0

            ? Math.max(len + relativeStart, 0)

            : Math.min(relativeStart, len);

 

    // Steps 9-10.

    var relativeEnd = parseInt(arguments[2] || len);

 

    // Step 11.

    var final = relativeEnd < 0

                ? Math.max(len + relativeEnd, 0)

                : Math.min(relativeEnd, len);

 

    // Step 12.

    for (; k < final; k++) {

        O[k] = value;

    }

 

    // Step 13.

    return O;

  };

}

相关链接

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Array.prototype.fill()

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