js与jquery常用数组方法总结
昨天被问数组方法的时候，问到sort()方法是否会改变原来的数组。本来我猜是不会，也是这么说，马上我又觉得，知识这种东西，不确定的时候直接说不确定或不知道就好，只是凭借着不确定的猜测或者是记忆，害人害己，于是我又回答不知道。结果果然。。。我记错了0.0 还是自己总结测试一下比较靠谱，印象也比较深刻。欢迎大家提出相关意见或建议，提前谢谢哈~
一.原生js方法
1.遍历数组 in(同时也是对象遍历属性的方法)
var a = [1, 2, 3]; for (x in a) { console.log(x); }
// 0
// 1
// 2
2.合并数组 concat
var a = [1, 2, 3], b = [4, 5, 6], c; c = b.concat(a); //将a加在b后,返回新数组，a和b并没有变。参数数量不限 console.log(b); // [4, 5, 6]
console.log(c); // [4, 5, 6, 1, 2, 3]
3.合并数组的值为字符串 join
var a = [1, 2, 3], b = a.join('*'); //默认为之间加上 , console.log(a); // [1, 2, 3] //a并没有变 console.log(b); // 1*2*3
参数为分隔符，默认为" , "分隔，当参数为' '时表示直接连接，常用于js中拼接html,如自定义弹窗，js生成form表单。
4.数组排序 sort
var a = [6, 2, 3, 'a', 'x', 20], b = a.sort(); //ASC表顺序，先看首位，因此20排在3前面 console.log(a); // [2, 20, 3, 6, "a", "x"] //a变化了 console.log(b); // [2, 20, 3, 6, "a", "x"] a.push('k'); console.log(b); // [2, 20, 3, 6, "a", "x", "k"] //a和b指向同一个对象，b相当于a的别名，所以 b 也变了
可以在参数里写排序规则函数, 如全是数字从小到大排序(注意返回值正负)
var a = [3, 2, 6, 20], b = a.sort(function(x, y) { return x - y; }); console.log(b);
当不全是数字的时候，会产生奇葩错误(NaN)，见下图
由此可知，注意运算符的正确用法还是很重要的。对于NaN，能少操作就少操作，毕竟是唯一一个js中不等于任何值的类型(Not a Number),包括它本身(可以用来判断一个变量是不是NaN,未初始化的变量是无类型的)。
5.数组的模拟栈(FILO) 和队列(FIFO) 方法(均改变原来数组)
var a = [6, 2, 3, 'a', 'x', 20], b = a.push('ab'), // 末尾添加元素，并返回新长度 c = a.pop(), // 删除并返回数组的最后一个元素 d = a.unshift('xy'), // 开头添加元素，并返回新长度 e = a.shift(); // 删除并返回数组的第一个元素 console.log(a); console.log(b); console.log(c); console.log(d); console.log(e);
可见这类方法添加元素则返回添加后长度， 删除元素则返回被删的那个可怜家伙(同splice)。
6.数组反序 reverse
var a = [6, 2, 3, 'a', 'x', 20], b = a.reverse(); // 返回a的引用 console.log(a); // [20, "x", "a", 3, 2, 6] console.log(b); // [20, "x", "a", 3, 2, 6]
7.取数组中需要的部分 slice
var a = [6, 2, 3, 'a', 'x', 20], b = a.slice(0, 2); //下标从0取到2(不包括2)，没有第二个参数则默认到末尾。第一个参数为负表示从末尾开始数。第一个参数小于第二个参数则为空。 console.log(a); console.log(b); // [6, 2] //b是a一部分的副本,a本身不变
8.修改数组 splice (既然是修改数组，肯定数组本身会变的啦)
var a = [1, 2, 3, 4], b = a.splice(0, 2, 6); console.log(a); // [6, 3, 4] console.log(b); // [1, 2] //b为被删掉的数组部分
a.splice(index, num, newItem1, newItem2...):index为开始选择的元素下标，num为接下来要删除元素的个数，newItem为接下来(在删完的地方)要添加的新元素(非必须)。这个方法用途最多，如
删除指定下标(2,也就是第三个)元素,此时不设置需要添加的newItem，而num设为1
var a = [1, 2, 3, 4], b = a.splice(2, 1); console.log(a); // [1, 2, 4] console.log(b); // [3]
在任意位置添加任意多个元素(如在下标2后添加两个元素'7','8'),此时num设为0
var a = [1, 2, 3, 4], b = a.splice(2, 0, 7, 8); console.log(a); console.log(b); //没有删除，b返回[]
根据元素值删除元素(结合jquery)
var a=[1,2,3,4]; a.splice($.inArray(2,a), 1); console.log(a); // [1, 3, 4]
plus:数组也是特殊的对象(但是拥有自己的方法，一般用下标访问)，因此同样也有对象的通用方法toString和valueOf
var a = [1, 2, [3,2], 4], b = a.toString(); // 转化为字符串(不管有多少层) console.log(a); // a本身不变 console.log(b);
var a = [1, 2, 4], b = a.valueOf(); // 返回原始值(其实还是它本身。。。) console.log(a); // a本身不变 console.log(b);
小结:综上所述，js数组的原生方法里面
修改自身的有: splice, pop, push, shift, unshift, sort, reverse
不修改自己身的: slice, concat, join
二.Jquery常用js方法
1.遍历
可以对所有的元素进行操作。如果想要满足条件退出，用return false( 绝大部分jquery方法都可以这么退出)。
$.each(arr, callback(key, val)); //可以链式调用，返回arr，为本身
var a = [1, 2, 3, 4]; $.each(a, function(key, val) { //以jQuery对象的方法调用，兼容性好;也可以用$(a)将a转化为jquery对象，然后以$(a).each(function(){})的形式调用,下面的方法同 console.log(a[key] + '下标为' + key + '值为' + val); });
//对应源码(jquery1.11.0下面同)
// Execute a callback for every element in the matched set.
// (You can seed the arguments with an array of args, but this is
// only used internally.
each: function( obj, callback, args ) { var value, i = 0, length = obj.length, isArray = isArraylike( obj ); if ( args ) { if ( isArray ) { for ( ; i < length; i++ ) { value = callback.apply( obj[ i ], args ); //第三个参数用于扩展obj元素的方法,一般不用 if ( value === false ) { break; } } } else { for ( i in obj ) { value = callback.apply( obj[ i ], args ); if ( value === false ) { break; } } } // A special, fast, case for the most common use of each } else { if ( isArray ) { for ( ; i < length; i++ ) { value = callback.call( obj[ i ], i, obj[ i ] ); if ( value === false ) { break; } } } else { for ( i in obj ) { value = callback.call( obj[ i ], i, obj[ i ] ); if ( value === false ) { break; } } } } return obj; }
2. 筛选
$.grep(arr, callback, invert)
invert为false表示对callback的筛选取反。 默认为true。
var a = [1, 2, 3, 4]; $.grep(a, function(val, key) { //不能链式调用，返回[],所以可以加上return实现链式,返回满足条件的副本 if (a[key] > 2) { console.log(key); } return val; });
常用做获取两个数组中相同(或不相同)的部分
var a= [1, 2, 3, 4], b=[1,3,5,7]; $.grep(a,function(val,key){ if(b.indexOf(val)>=0){ return val; } },false);
//jquery源码 grep: function( elems, callback, invert ) { var callbackInverse, matches = [], i = 0, length = elems.length, callbackExpect = !invert; // Go through the array, only saving the items // that pass the validator function for ( ; i < length; i++ ) { callbackInverse = !callback( elems[ i ], i ); //如果callback没有设置return，那么返回undefined(!undefined还是undefined) if ( callbackInverse !== callbackExpect ) { matches.push( elems[ i ] ); //只添加满足条件的,内部实现为push方法 } } return matches; }
3.转换
$.map(arr,callback(key,val))
var a = [1, 2, 3, 4]; $.map(a, function(val, key) { //不能链式调用，返回[],同grep加上return即可放回副本 if (a[key] > 2) { a[key]=val+1; } return val; //可以链式调用，返回处理后的数组(也可用于筛选) });
// arg is for internal usage only map: function( elems, callback, arg ) { var value, i = 0, length = elems.length, isArray = isArraylike( elems ), ret = []; // Go through the array, translating each of the items to their new values if ( isArray ) { for ( ; i < length; i++ ) { value = callback( elems[ i ], i, arg ); if ( value != null ) { ret.push( value ); } } // Go through every key on the object, } else { for ( i in elems ) { value = callback( elems[ i ], i, arg ); //如果callback没有返回值，那么value就是undefined if ( value != null ) { ret.push( value ); } } } // Flatten any nested arrays return concat.apply( [], ret ); //如果callback没有返回值，那么value就是[]
}
背景标白的区域为与each方法不同的地方，可以简单的理解为返回对象是否是副本(map是副本)，另外map是为数组或类数组对象量身定做的，而each可以应用于全部对象。
4.合并
$.merge(arr1,arr2) arr1后面加上arr2后返回arr1
var a=[1,2,3], b=[4,5,6]; $.merge(a,b); //可以有多个参数(居然不报错!)，但是第三个及以后的没用(test in FF and Chrome)
//jquery源码 merge: function( first, second ) { var len = +second.length, j = 0, i = first.length; while ( j < len ) { first[ i++ ] = second[ j++ ]; } // Support: IE<9 // Workaround casting of .length to NaN on otherwise arraylike objects (e.g., NodeLists) if ( len !== len ) { while ( second[j] !== undefined ) { first[ i++ ] = second[ j++ ]; } } first.length = i; return first; }
源码的第二行有个+，最开始我以为是显式声明非负值，后来看到了arraylike，于是测试了极端情况如下:
var ax; ax.length //报错，type error +ax.length //报错，type error var ab={}; //空对象作为类空数组对象 ab.length //undefined +ab.length //NaN var ab=[]; ab.length //0 +ab.length //0 var ab=null; ab.length //报错，type error +ab.length //报错，type error
忽然觉得然并卵。。。好吧，也许是我计较太多。如果有谁看到有关的解释，麻烦留下言，谢谢~
5.过滤相同元素
$.unique(arr)//过滤Jquery对象数组中重复的元素(内部实现为===)(不同版本不一样，不要用)
var a = [ 1 , 1 , 2 , 3 , 7 , 4 , 5 , 5 , 6 , 6 ]; $.unique(a)
jquery1.11.0运行结果
jquery1.8.3运行结果
好神奇啊，有木有！看一下源码保险~
//jquery1.11.0 jQuery.unique = Sizzle.uniqueSort; Sizzle.uniqueSort = function( results ) { var elem, duplicates = [], j = 0, i = 0; // Unless we *know* we can detect duplicates, assume their presence hasDuplicate = !support.detectDuplicates; sortInput = !support.sortStable && results.slice( 0 ); results.sort( sortOrder ); if ( hasDuplicate ) { while ( (elem = results[i++]) ) { if ( elem === results[ i ] ) { //用=== j = duplicates.push( i ); } } while ( j-- ) { results.splice( duplicates[ j ], 1 ); //用splice实现 } } // Clear input after sorting to release objects // See https://github.com/jquery/sizzle/pull/225 sortInput = null; return results; };
//jquery1.8.3 jQuery.unique = Sizzle.uniqueSort; Sizzle.uniqueSort = function( results ) { var elem, duplicates = [], i = 1, j = 0; hasDuplicate = baseHasDuplicate; results.sort( sortOrder ); if ( hasDuplicate ) { for ( ; (elem = results[i]); i++ ) { if ( elem === results[ i - 1 ] ) { j = duplicates.push( i ); } } while ( j-- ) { results.splice( duplicates[ j ], 1 ); } } return results; };
对应红色的字体为新增或者修改的，然而并看不出什么，调试一下进入，会发现问题居然在sortOrder上!坑啊!继续找~~~
//jquery1.11.0 //定义时 sortOrder = function(a, b) { if (a === b) { hasDuplicate = true; } return 0; }; //setDocument里面 sortOrder = hasCompare ? function(a, b) { // Flag for duplicate removal if (a === b) { hasDuplicate = true; return 0; } // Sort on method existence if only one input has compareDocumentPosition var compare = !a.compareDocumentPosition - !b.compareDocumentPosition; if (compare) { return compare; } // Calculate position if both inputs belong to the same document compare = (a.ownerDocument || a) === (b.ownerDocument || b) ? a.compareDocumentPosition(b) : // Otherwise we know they are disconnected 1; // Disconnected nodes if (compare & 1 || (!support.sortDetached && b.compareDocumentPosition(a) === compare)) { // Choose the first element that is related to our preferred document if (a === doc || a.ownerDocument === preferredDoc && contains(preferredDoc, a)) { return -1; } if (b === doc || b.ownerDocument === preferredDoc && contains(preferredDoc, b)) { return 1; } // Maintain original order return sortInput ? (indexOf.call(sortInput, a) - indexOf.call(sortInput, b)) : 0; } return compare & 4 ? -1 : 1; } : function(a, b) { // Exit early if the nodes are identical if (a === b) { hasDuplicate = true; return 0; } var cur, i = 0, aup = a.parentNode, bup = b.parentNode, ap = [a], bp = [b]; // Parentless nodes are either documents or disconnected if (!aup || !bup) { return a === doc ? -1 : b === doc ? 1 : aup ? -1 : bup ? 1 : sortInput ? (indexOf.call(sortInput, a) - indexOf.call(sortInput, b)) : 0; // If the nodes are siblings, we can do a quick check } else if (aup === bup) { return siblingCheck(a, b); } // Otherwise we need full lists of their ancestors for comparison cur = a; while ((cur = cur.parentNode)) { ap.unshift(cur); } cur = b; while ((cur = cur.parentNode)) { bp.unshift(cur); } // Walk down the tree looking for a discrepancy while (ap[i] === bp[i]) { i++; } return i ? // Do a sibling check if the nodes have a common ancestor siblingCheck(ap[i], bp[i]) : // Otherwise nodes in our document sort first ap[i] === preferredDoc ? -1 : bp[i] === preferredDoc ? 1 : 0; };
//jquery 1.8.3 sortOrder = docElem.compareDocumentPosition ? function( a, b ) { if ( a === b ) { hasDuplicate = true; return 0; } return ( !a.compareDocumentPosition || !b.compareDocumentPosition ? a.compareDocumentPosition : a.compareDocumentPosition(b) & 4 ) ? -1 : 1; } : function( a, b ) { // The nodes are identical, we can exit early if ( a === b ) { hasDuplicate = true; return 0; // Fallback to using sourceIndex (in IE) if it's available on both nodes } else if ( a.sourceIndex && b.sourceIndex ) { return a.sourceIndex - b.sourceIndex; } var al, bl, ap = [], bp = [], aup = a.parentNode, bup = b.parentNode, cur = aup; // If the nodes are siblings (or identical) we can do a quick check if ( aup === bup ) { return siblingCheck( a, b ); // If no parents were found then the nodes are disconnected } else if ( !aup ) { return -1; } else if ( !bup ) { return 1; } // Otherwise they're somewhere else in the tree so we need // to build up a full list of the parentNodes for comparison while ( cur ) { ap.unshift( cur ); cur = cur.parentNode; } cur = bup; while ( cur ) { bp.unshift( cur ); cur = cur.parentNode; } al = ap.length; bl = bp.length; // Start walking down the tree looking for a discrepancy for ( var i = 0; i < al && i < bl; i++ ) { if ( ap[i] !== bp[i] ) { return siblingCheck( ap[i], bp[i] ); } } // We ended someplace up the tree so do a sibling check return i === al ? siblingCheck( a, bp[i], -1 ) : siblingCheck( ap[i], b, 1 ); };
很多是不是？有木有觉得瞬间被我坑了?啊哈，其实只要继续调试的时候断点设置好，你就会发现~~~没有比这更坑的了！它们都是循环的！1.8.3里面就在第一个function里面转来转去，手都点酸了也没看到出来，1.11.0整体循环，有参数的个数那么多次。
最后的结论是:还是不要用这个不靠谱的函数了。如果需要类似的功能，用原生js手动写就好。同时说明了关注更新的重要性，不过程序猿也不一定有那么长的时间去关注每一次的更新，那么就一定要准确的了解自己手头的版本，最好是空闲时对用到的功能测试一下，看下源码，网上得来终觉浅啊~
6.判断
$.inArray(val,arr) 判断val是否在arr里面
var a = [1, 2, 3, 4]; $.inArray(2, a); //有的话返回下标，没有的话返回-1
//对应源码 inArray: function(elem, arr, i) { var len; if (arr) { if (indexOf) { return indexOf.call(arr, elem, i); //实际实现 } len = arr.length; i = i ? i < 0 ? Math.max(0, len + i) : i : 0; for (; i < len; i++) { // Skip accessing in sparse arrays if (i in arr && arr[i] === elem) { //一般尽可能用===而杜绝==可能带来的隐式转换 return i; } } } return -1; }
7.元素转数组
$.makeArray()将一个类数组对象转换为真正的数组对象。(所谓"类数组对象"就是一个常规的Object对象，但它和数组对象非常相似：具备length属性，并以0、1、2、3……等数字作为属性名。不过它毕竟不是数组，没有从数组的原型对象上继承下来的内置方法(例如：push()、 sort()等)。)
$.toArray()将所有DOM元素恢复成数组。(其实用选择器取的时候就是很自然的数组的形式)
这两个实际用得太少了就不具体分析了，知道有这玩意就行吧。
The Array.from() method creates a new Array instance from an array-like or iterable
console.log(Array.from('foo'));
// expected output: Array ["f", "o", "o"]
console.log(Array.from([1, 2, 3], x => x + x));
// expected output: Array [2, 4, 6]
三.补充
1.清空数组
方法1:length设为0 (js身为弱变量类型语言的体现之一，array的length属性可写)(效率比较低)
方法2:直接指向[]的引用 (如闭包销毁指向null一样，垃圾回收会自动回收空间)(效率比较高)
2.兼容性
IE8下
$.inArray 代替 indexOf
$.grep代替Array.prototype.filter
3.注意事项
一般情况下用$.functionName(obj,callback)的形式调用jquery方法的兼容性比较好，比如我曾遇到IE8及以下不能识别$(dom).val().trim()的情况，显示trim is not a function，然而改为$.trim($(dom).val())就没问题。
前面那种情况实际是string调用trim方法(如果加上call或者apply注入trim方法可以过，但是必要嘛？)，后面是jquery对象调用trim方法。
最后再啰嗦一句，欢迎大家的意见和建议，帮我纠错，共同进步，谢谢！
附:之前学习权威指南的笔记图
4. Much More（reduce、reduceRight、filter）
MDN：https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/of
1、The Array.of() method creates a new Array instance with a variable number of arguments, regardless of number or type of the arguments.
Array.of(7); // [7] Array.of(1, 2, 3); // [1, 2, 3] Array(7); // [ , , , , , , ] Array(1, 2, 3); // [1, 2, 3]
2、The copyWithin() method shallow copies part of an array to another location in the same array and returns it, without modifying its size.
[1, 2, 3, 4, 5].copyWithin(-2); // [1, 2, 3, 1, 2] [1, 2, 3, 4, 5].copyWithin(0, 3); // [4, 5, 3, 4, 5] [1, 2, 3, 4, 5].copyWithin(0, 3, 4); // [4, 2, 3, 4, 5] [1, 2, 3, 4, 5].copyWithin(-2, -3, -1); // [1, 2, 3, 3, 4] [].copyWithin.call({length: 5, 3: 1}, 0, 3); // {0: 1, 3: 1, length: 5}
3、The entries() method returns a new Array Iterator object that contains the key/value pairs for each index in the array.
var array1 = ['a', 'b', 'c']; var iterator1 = array1.entries(); console.log(iterator1.next().value); // expected output: Array [0, "a"] console.log(iterator1.next().value); // expected output: Array [1, "b"]
4、The every() method tests whether all elements in the array pass the test implemented by the provided function.
function isBelowThreshold(currentValue) { return currentValue < 40; } var array1 = [1, 30, 39, 29, 10, 13]; console.log(array1.every(isBelowThreshold)); // expected output: true
5、The fill() method fills all the elements of an array from a start index to an end index with a static value.
var array1 = [1, 2, 3, 4]; // fill with 0 from position 2 until position 4 console.log(array1.fill(0, 2, 4)); // expected output: [1, 2, 0, 0] // fill with 5 from position 1 console.log(array1.fill(5, 1)); // expected output: [1, 5, 5, 5] console.log(array1.fill(6)); // expected output: [6, 6, 6, 6]
6、The filter() method creates a new array with all elements that pass the test implemented by the provided function.
var words = ['spray', 'limit', 'elite', 'exuberant', 'destruction', 'present']; const result = words.filter(word => word.length > 6); console.log(result); // expected output: Array ["exuberant", "destruction", "present"]
7、The find() method returns the value of the first element in the array that satisfies the provided testing function. Otherwise undefined is returned.
var array1 = [5, 12, 8, 130, 44]; var found = array1.find(function(element) { return element > 10; }); console.log(found); // expected output: 12
8、The includes() method determines whether an array includes a certain element, returning true or false as appropriate.
var array1 = [1, 2, 3]; console.log(array1.includes(2)); // expected output: true var pets = ['cat', 'dog', 'bat']; console.log(pets.includes('cat')); // expected output: true console.log(pets.includes('at')); // expected output: false
9、The keys() method returns a new Array Iterator object that contains the keys for each index in the array.
var arr = ['a', 'b', 'c']; var iterator = arr.keys(); console.log(iterator.next()); // { value: 0, done: false } console.log(iterator.next()); // { value: 1, done: false } console.log(iterator.next()); // { value: 2, done: false } console.log(iterator.next()); // { value: undefined, done: true }
10、The reduce() method applies a function against an accumulator and each element in the array (from left to right) to reduce it to a single value.
const array1 = [1, 2, 3, 4]; const reducer = (accumulator, currentValue) => accumulator + currentValue; // 1 + 2 + 3 + 4 console.log(array1.reduce(reducer)); // expected output: 10 // 5 + 1 + 2 + 3 + 4 console.log(array1.reduce(reducer, 5)); // expected output: 15
11、The reduceRight() method applies a function against an accumulator and each value of the array (from right-to-left) to reduce it to a single value.
const array1 = [[0, 1], [2, 3], [4, 5]].reduceRight( (previousValue, currentValue) => previousValue.concat(currentValue) ); console.log(array1); // expected output: Array [4, 5, 2, 3, 0, 1]
12、The some() method tests whether at least one element in the array passes the test implemented by the provided function.
function isBiggerThan10(element, index, array) { return element > 10; } [2, 5, 8, 1, 4].some(isBiggerThan10); // false [12, 5, 8, 1, 4].some(isBiggerThan10); // true
