标签：merge asc str rev block fine def developer 数组
let isObject = {};
console.log(JSON.stringify(isObject) == ‘{}‘);
let listObject = { a: 1, b: 3, c: 4 };
function isEmptyObject() {
for(let key in listObject) {
return false;
}
return true;
}
console.log(isEmptyObject());
function isEmptyObject2(obj) { return Object.keys(obj).length == 0; } console.log(isEmptyObject2(isObject));
console.log(isObject.id == null);
var inventory = [ {name: ‘apples‘, quantity: 2}, {name: ‘bananas‘, quantity: 0}, {name: ‘cherries‘, quantity: 5} ]; function findCherries(fruit) { return function(value){ return value.name == fruit } } console.log(inventory.find(findCherries(‘cherries‘))); // { name: ‘cherries‘, quantity: 5 }
Object.values()方法返回一个给定对象自身的所有可枚举属性值的数组，值的顺序与使用for...in循环的顺序相同 ( 区别在于 for-in 循环枚举原型链中的属性 )。
var obj = { foo: ‘bar‘, baz: 42 }; console.log(Object.values(obj)); // [‘bar‘, 42] // array like object var obj = { 0: ‘a‘, 1: ‘b‘, 2: ‘c‘ }; console.log(Object.values(obj)); // [‘a‘, ‘b‘, ‘c‘] // array like object with random key ordering // when we use numeric keys, the value returned in a numerical order according to the keys var an_obj = { 100: ‘a‘, 2: ‘b‘, 7: ‘c‘ }; console.log(Object.values(an_obj)); // [‘b‘, ‘c‘, ‘a‘] // getFoo is property which isn‘t enumerable var my_obj = Object.create({}, { getFoo: { value: function() { return this.foo; } } }); my_obj.foo = ‘bar‘; console.log(Object.values(my_obj)); // [‘bar‘] // non-object argument will be coerced to an object console.log(Object.values(‘foo‘)); // [‘f‘, ‘o‘, ‘o‘]
Object.values()详细参考地址：《MDN：Object.values(obj)》
[].slice.call(arguments)/* 该方法可以将类数组对象转换为数组，所谓类数组对象，就是含 length 和索引属性的对象 * 返回的数组长度取决于对象 length 属性的值，并且非索引属性的值或索引大于 length 的值都不会被返回到数组中 * Array.prototype.slice.call(obj,start,end) start:方法中slice截取的开始位置，end终止位置，默认从0开始 * */ let testObject = { 0: ‘a‘, 1: ‘b‘, 2: ‘c‘, name: ‘admin‘, length: 3, }; /* 对象中必须定义length，且属性值不能为非数字，非数字无法返回 */ console.log(Array.prototype.slice.call(testObject)); /* 或者简写为[].slice.call(testObject) */ console.log([].slice.call(testObject));
/* Array、Set、Map 和字符串都是可迭代对象（WeakMap/WeakSet 并不是可迭代对象） * 这些对象都有默认的迭代器，即具有 Symbol.iterator 属性 * 所有通过生成器创建的迭代器都是可迭代对象 * 可以用 for of 循环 * */ let testObject2 = { 0: ‘a‘, 1: ‘b‘, 2: ‘c‘, name: ‘admin‘, length: 3, }; console.log(Array.from(testObject2));
let temporaryArray3 = [1,2,1,2,3]; console.log(temporaryArray3 instanceof Array); console.log(temporaryArray3.constructor == Array); console.log(Array.isArray(temporaryArray3)); console.log(Object.prototype.toString.call(temporaryArray3) === "[object Array]");
let transformObject = Object.assign({}, temporaryArray3); console.log(transformObject); let transformObject2 = {...temporaryArray3}; console.log(transformObject2);
较常用的对象深拷贝方法：
let copyObject = JSON.parse(JSON.stringify(obj));
assign对对象分配赋值,实现浅拷贝，但是它有一个特殊的地方，可以处理第一层的深拷贝。
assign(targetObject, obj, obj1) assign会改变targetObject的值，较好的做法就是将targetObject定义为空对象{}
assign是将这个3者合并，若有相同的属性，后面的属性会覆盖前面对象的属性
let temporaryObject2 = {a: 1, d: {e: 3}};
let temporaryObject3 = {b: 1,a: 2};
let mergeObject = Object.assign({}, temporaryObject2, temporaryObject3);
console.log(mergeObject);
/* mergeObject.d.e不会改变temporaryObject2里a的值，但会改变temporaryObject2里e的值 */
mergeObject.a = 5;
mergeObject.d.e = 5;
console.log(mergeObject);
let copyArray1 = copyArray.slice(0);
let copyArray2 = copyArray.concat();
// 以chrome为例 new Date(); // Mon Oct 23 2017 23:38:02 GMT+0800 (CST) new Date(false); // Thu Jan 01 1970 08:00:00 GMT+0800 (CST) new Date(0); // Thu Jan 01 1970 08:00:00 GMT+0800 (CST) new Date(null); // Thu Jan 01 1970 08:00:00 GMT+0800 (CST) new Date(‘‘); // Invalid Date new Date(undefined); // Invalid Date
详情参考：你可能不知道的 Date 类
data.forEach(ele => { let parentId = ele.parentId; if (parentId === 0) { //是根元素的hua ,不做任何操作,如果是正常的for-i循环,可以直接continue. } else { //如果ele是子元素的话 ,把ele扔到他的父亲的child数组中. data.forEach(d => { if (d.id === parentId) { let childArray = d.child; if (!childArray) { childArray = [] } childArray.push(ele); d.child = childArray; } }) } }); //去除重复元素 data = data.filter(ele => ele.parentId === 0); console.log(‘最终等到的tree结构数据: ‘, data);
先看下网上一个简单的代码片段：
let blob = new Blob([res], { type: `application / pdf` //word文档为msword,pdf文档为pdf }); let objectUrl = URL.createObjectURL(blob); let link = document.createElement("a"); let fname = `我的文档`; //下载文件的名字 link.href = objectUrl; link.setAttribute("download", fname); document.body.appendChild(link); link.click();
全面：
/** * @param {String} resource 文件流 * @param {String} fileType 文件类型 * @param {String} fileName 文件名 * */ var downloadBlob=function(resource,fileType,fileName){ var data = new Blob([resource],{ type:fileType }); if(‘download‘ in document.createElement(‘a‘)){ //非IE var downloadUrl = window.URL.createObjectURL(data); var anchor = document.createElement("a"); anchor.href = downloadUrl; anchor.download = fileName; anchor.style.display = ‘none‘; document.body.appendChild(anchor); anchor.click(); window.URL.revokeObjectURL(anchor.href); document.body.removeChild(anchor); }else{ //IE10+下载 navigator.msSaveBlob(data, fileName); } }
调用方式：
downloadBlob(res,‘application/pdf‘,‘文档名称‘)
标签：merge asc str rev block fine def developer 数组
原文地址：https://www.cnblogs.com/moqiutao/p/9848991.html
