语法:
_.filter(list, predicate, [context])
说明:
对list集合的每个成员依次进行匹配(根据predicate迭代函数检测),返回匹配成功的集合
- list可以为数组,对象,字符串和arguments
- predicate会传第三个参数value, key, list(参数名可自定义)
- predicate函数需要返回值
- context可以改变predicate函数内部的this
代码示例:
示例一:filter对数组,对象,字符串,arguments进行操作并返回匹配成功的数据
var result; // 操作数组 result = _.filter([1, 2, 3], function (value) { return value % 2 === 1; }); console.log(result) //=> [1, 3] // 操作对象 result = _.filter({ one: ‘一‘, two: ‘二‘, three: ‘三‘, num: 123, bool: false }, function (value) { return typeof value === "string"; }); console.log(result) //=> ["一", "二", "三"] // 操作复杂的对象 var obj = { levelA: { level0: ‘level0‘, level1: ‘level1‘ }, levelB: ‘一‘, levelC: 1, levelD: { level3: ‘level3‘ } } result = _.filter(obj, function (value) { return typeof value === "object"; }); console.log(result) //=> [{level0: "level0", level1: "level1", {level3: ‘level3‘}}] // 操作字符串(此处将字符拆分为数组) result = _.filter(‘123‘, function (value) { return value === ‘2‘ || value === ‘3‘; }); console.log(result) //=> ["2", "3"] //操作arguments function abc() { result = _.filter(arguments, function (value) { return value % 2 === 1; }); console.log(result); //=> [1, 3] } abc(1, 2, 3);
示例二:predicate函数传递的参数(函数内部需要return返回值,否则返回[])
var result; //数组的情况 result = _.filter([1, 2, 3], function (value, key, list) { console.log(value, key, list); //=> 1 0 [1, 2, 3] //=> 2 1 [1, 2, 3] //=> 3 2 [1, 2, 3] }); console.log(result) //=> [] //对象的情况 result = _.filter({one: ‘一‘, two: ‘二‘, three: ‘三‘}, function(value, key, list){ console.log(value, key, list); //=> 一 one Object {one: "一", two: "二", three: "三"} //=> 二 two Object {one: "一", two: "二", three: "三"} //=> 三 three Object {one: "一", two: "二", three: "三"} }); console.log(result) //=> []
示例三:context可以改变predicate内部的this
var result; // 数组的情况 result = _.filter([1, 2, 3], function (value, key, list) { console.log(this); //=> [1, 2, 3] this是数组 }, [1, 2, 3]); // 对象的情况 result = _.filter([1, 2, 3], function (value, key, list) { console.log(this); //=> Object {no: 10} this是对象 }, { "no": 10 }); // 字符串的情况 result = _.filter([1, 2, 3], function (value, key, list) { console.log(this); //=> String {0: "1", 1: "2", 2: "3", length: 3, [[PrimitiveValue]]: "123"} // this是将字符串拆分后的对象 }, "123");
_.select的功能和_.filter是一样的
var result = _.filter([1, 2, 3], function (value, key, list) { return value % 2 === 1; }); console.log(result) //=> [1, 3]
特殊情况
示例一:list的特殊情况
//例如:null,undefined,0,true,this等; var result = _.filter(null, function (value, key, list) { return true; }); console.log(result) //=> []
示例二:predicate函数的this为window全局对象的情况
// 例如:null,undefined,window,this等 var result = _.filter([1, 2, 3], function (value, key, list) { console.log(this); //=> this是window全局对象 }, null);
list参数可为真假值?
var result = _.filter([1, true, ‘1‘, 0, undefined, null]); console.log(result) //=> [1, true, "1"]
predicate还有其他写法?
示例一:predicate参数为空的时候
var result = _.filter({x: 1, y: 2}); console.log(result) //=> [1, 2]
示例二:predicate参数为一个字符的时候
var result = _.filter([{x: 1}, {y: 2}], ‘x‘); console.log(result) //=> [{x: 1}]
示例三:predicate参数为对象的时候
var obj = [ {x: 1, y: 2}, {x: 1}, {y: 2, z: 3} ] var result = _.filter(obj, {x: 1}); console.log(result) //=> [{x: 1, y: 2},{x: 1}]
时间: 2024-10-16 20:38:58