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Array.prototype.indexOf = function(val) {

for (var i = 0; i < this.length; i++) {

if (this[i] == val) return i;

}

return -1;

};

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Array.prototype.remove = function(val) {

var index = this.indexOf(val);

if (index > -1) {

this.splice(index, 1);

}

};

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var emp = ['abs','dsf','sdf','fd']

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emp.remove('fd');

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//刪除起始下標為1，長度為1的一個值(len設定1，如果為0，則陣列不變)

var arr = ['a','b','c','d'];

arr.splice(1,1);

console.log(arr);

//['a','c','d'];

//刪除起始下標為1，長度為2的一個值(len設定2)

var arr2 = ['a','b','c','d']

arr2.splice(1,2);

console.log(arr2);

//['a','d']

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//替換起始下標為1，長度為1的一個值為‘ttt'，len設定的1

var arr = ['a','b','c','d'];

arr.splice(1,1,'ttt');

console.log(arr);  

//['a','ttt','c','d']

var arr2 = ['a','b','c','d'];

arr2.splice(1,2,'ttt');

console.log(arr2);  

//['a','ttt','d'] 替換起始下標為1，長度為2的兩個值為‘ttt'，len設定的1

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var arr = ['a','b','c','d'];

arr.splice(1,0,'ttt');

console.log(arr);  

//['a','ttt','b','c','d'] 表示在下標為1處新增一項'ttt'<span style="font-size:14px;font-family:Arial, Helvetica, sans-serif;background-color:rgb(255,255,255);"> </span>

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var arr = ['a','b','c','d'];

delete arr[1];

arr;

//["a", undefined × 1, "c", "d"] 中間出現兩個逗號，陣列長度不變，有一項為undefined