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About the usage of js array filter

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Release: 2018-07-14 17:15:40
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This article mainly introduces the use of js array filter method, which has certain reference value. Now I share it with everyone. Friends in need can refer to it

filter()方法使用指定的函数测试所有元素,并创建一个包含所有通过测试的元素的新数组。

filter()基本语法:
        arr.filter(callback[, thisArg])

filter()参数介绍:
        参数名    说明
        callback   用来测试数组的每个元素的函数。调用时使用参数 (element, index, array)
        返回true表示保留该元素(通过测试),false则不保留。
        thisArg    可选。执行 callback 时的用于 this 的值。

filter()用法说明:

        filter 为数组中的每个元素调用一次 callback 函数,并利用所有使得 callback 返回 true 或 等价于 true 的值 的元素创建一个新数组。
        callback 只会在已经赋值的索引上被调用,对于那些已经被删除或者从未被赋值的索引不会被调用。那些没有通过 callback 测试的元素会被跳过,不会被包含在新数组中。

        callback 被调用时传入三个参数:

        元素的值
        元素的索引
        被遍历的数组
        如果为 filter 提供一个 thisArg 参数,则它会被作为 callback 被调用时的 this 值。否则,callback 的this 值在非严格模式下将是全局对象,严格模式下为 undefined。

        filter 不会改变原数组。

        filter 遍历的元素范围在第一次调用 callback 之前就已经确定了。在调用 filter 之后被添加到数组中的元素不会被 filter 遍历到。
        如果已经存在的元素被改变了,则他们传入 callback 的值是 filter 遍历到它们那一刻的值。被删除或从来未被赋值的元素不会被遍历到。
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Example 1--Filtering Values ​​less than 10;

 function isBigEnough(element) {   
    return element >= 10;
 }
 var filtered = [12, 5, 8, 130, 44].filter(isBigEnough);
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Example 2--Filtering data in objects; Mostly used for filtering functions;

    var arr = [
      {
        name: '小米',
        code: '01'
      },
      {
        name: "小米米",
        code: '02'
      },
      {
        name: "小明",
        code: '03'
      },
      {
        name: "大明",
        code: '"04"'
      }
    ]
    var newArr = arr.filter((v) => { return v.name.includes('明') })
    console.log(newArr);  //         {
                          //         name: "小明",
                          //          code: '03'
                          //         },
                          //         {
                          //          name: "大明",
                          //          code: '"04"'
                          //         }
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