Note: Some of the answers are self-collated and the correctness is unknown. Run the result part of the code by hand, no problem.
Get page element position and width?
- element.clientWidth = content + padding
- element.clientHeight = content + padding
- Element. GetBoundingClientRect () returns a value
- Left: The distance between the left edge of the bounding box and the left side of the page
- Right: The distance between the right border of the bounding box and the left side of the page
- Top: The distance between the top of the page and the edge of the bounding box other than the border
- Bottom: Easy distance from the top of the page beyond the border below the bounding box
- width: content + padding + border
- height: content + padding + border
- Notice how margins merge when margins are set
RequestAnimationFrame principles? Is it synchronous or asynchronous?
Asynchronous, incoming functions are called before redrawing.
- http://web.jobbole.com/91578/
- https://my.oschina.net/bghead/blog/850692
- http://www.zhangxinxu.com/wordpress/2013/09/css3-animation-requestanimationframe-tween-%E5%8A%A8%E7%94%BB%E7%AE%97%E6%B3 % 95 /
Js event mechanism? How does an event propagate by clicking a button on the screen?
Capture the bubbling
The following code outputs the result? Why is that?
Function.prototype.a = 'a';
Object.prototype.b = 'b';
function Person(){};
var p = new Person();
console.log('p.a: '+ p.a); // p.a: undefined
console.log('p.b: '+ p.b); // p.b: b
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The following code outputs the result? Why is that?
const person = {
namea: 'menglinghua'.say: function (){
return function (){
console.log(this.namea); }; }}; person.say()();// undefined
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const person = {
namea: 'menglinghua'.say: function (){
return (a)= > {
console.log(this.namea); }; }}; person.say()();// menglinghua
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The following code outputs the result? Why is that?
setTimeout((a)= > console.log('a'), 0);
var p = new Promise((resolve) = > {
console.log('b');
resolve();
});
p.then((a)= > console.log('c'));
p.then((a)= > console.log('d'));
console.log('e');
// result: b e C D a
Trick()> Promise callback >setTimeout>setImmediate
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async function async1() {
console.log("a");
await async2(); // After this statement, await will get rid of the current thread, add the following code to the task queue, and continue with the synchronization code following the function
console.log("b");
}
async function async2() {
console.log( 'c');
}
console.log("d");
setTimeout(function () {
console.log("e");
},0);
async1();
new Promise(function (resolve) {
console.log("f");
resolve();
}).then(function () {
console.log("g");
});
console.log('h');
// Who knows why the result is different ?????????????
D a C f h g b e
D a C f h b g e
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Js bind Hand write a bind method?
// Code from the book "javaScript Patterns"
if (typeof Function.prototype.bind === "undefined") {Function.prototype.bind = function (thisArgs){
var fn = this,
slice = Array.prototype.slice,
args = slice.call(arguments.1);
return function (){
return fn.apply(thisArgs, args.concat(slice.call(arguments))); }}}Copy the code
Vue implementation of on,emit,off,once, handwritten code.
// Reference vue source code implementation
var EventEmiter = function (){
this._events = {};
};
EventEmiter.prototype.on = function (event, cb){
if (Array.isArray(event)){
for (let i = 0, l = event.length; i < l; i++){
this.on(event[i], cb); }}else{(this._events[event] || (this._events[event] = [])).push(cb);
}
return this;
};
EventEmiter.prototype.once = function (event, cb){
function on () {
this.off(event, cb);
cb.apply(this.arguments);
}
on.fn = cb;
this.on(event, on);
return this;
};
EventEmiter.prototype.off = function (event, cb){
if (!arguments.length){
this._events = Object.create(null);
return this;
}
if (Array.isArray(event)){
for (let i = 0, l = event.length; i < l; i++){
this.off(event[i],cb);
}
return this;
}
if(! cb){this._events[event] = null;
return this;
}
if (cb){
let cbs = this._events[event];
let i = cbs.length;
while(i--){
if (cb === cbs[i] || cb === cbs[i].fn){
cbs.splice(i, 1);
break; }}return this; }}; EventEmiter.prototype.emit =function (event){
let cbs = this._events[event];
let args = Array.prototype.slice.call(arguments.1);
if (cbs){
for (let i = 0, l = cbs.length; i < l; i++){
cbs[i].apply(this,args); }}};Copy the code
Js double linked list, handwritten code?
Vue’s bidirectional binding mechanism? Detailed introduction.
What actions cause the browser to redraw and rearrange?
- postion:absolute; left:100px; Will it cause?
- translateX:100px; Will it cause?
- Does getBoundingClientRect cause?
- Can getClientWidth and getClientHeight be caused?