JavaScript 学习笔记

## Values


Object to bool,全部转换为True,包括 [] {}和new Boolean(false)

to string 首先调用toString(),如果没有然后调用valueOf()

to number 首先调用valueOf(),如果没有然后调用toString()

## Array

Array.sort([func]) // function cmp(a, b) {return a – b;}, implace
Array.concat(val or array) // combination of python append and extend, will not recursively smash array, return new
Array.slice(a, b) // allow negative
Array.splice(a, b, replacements…) // both a and b are inclusive
indexOf/lastIndexOf // return the first find index or -1 if not found
forEach // no way to good stop the iteration
map // return a new array
filter //return the selected elements
every/some // return true or false, return immediately after the result is dicided
reduce //reduce(function(a, b) {}, initial_value), when not supplied, the first element is used as initial value on empty array, no initial value will throw error

## ES5 functional array methods

they are both defined as Array.prototype.method and Array.method in firefox

### common pattern

array.method(function(value, index, array) {}, this) // second parameter is treated as this in the function

### using strings as arrays, parameters)

## this

### normal function

in ES3 and ES5, this is window by default.
in ES5 strict mode, this is undefined.
in ES6 arrow function, this is inherited from outer function

### constructor function

function MyClass(x, y) {
this.x = x;
this.y = y;

`var m = new MyClass(3, 5);`

`this` is the new constructed object, But, if something is returned from the constructor, then the temporary object is thrown

function MyOtherClass(x, y) {
return new MyClass(x, y);

var m = new MyOtherClass(x, y);

### method function

point.setX = function (x) {
this.x = x;

`this` is the object

#### tricky closure

function constfuncs() {
var funcs = [];
for (var i = 0; i < 10; i++) { funcs[i] = function() {return i;} // they refers to only one i in the closure, which is 10 in the end } return funcs; } var funcs = constfuncs(); funcs[5]() // returns 10, ``` ### call and apply `, params...)` is equal to obj.func(params...) `func.apply(obj, [params...])` `func.bind(obj)` will return a function with `this` bound as obj to the function call any method against null or undefined will result in TypeError   by default `this` for a function in strict mode is undefined   + prefer both operands to be numbers, comparison prefers both operands to be strings   if a property is not found in a object, it's looked up in the prototype, if not, it's looked up object created by new 's prototype is the constructor's prototype object created by     # class   if two instances inherited from the same prototype, we say then are inherited from the same class. by default, the prototype is constructor's prototype   ## subclassing   SubClass.prototype = Object.create(Base.prototype) SubClass.prototype.constructor = SubClass   # Regular Expression   syntax: /regexp/modifier   Modifiers:   i ignore case g global, if not sepcified, return only one match m multiline   String expression methods: return first matched index or -1 String.replace(pattern, replacement) back reference is used as $n, replacement can be a function String.match(pattern) return an array of matched groups, [0] is the whole match, [n] being each group String.split(pattern) return a splited elements   Regexp methods:   regexp.exec(String) equals to String.match(regexp) regexp.test(String) true or false regexp.exec(String) can be called multitimes for a string when regexp is not global mode. Each returns the   # Date   ## Constructs   new Data(); new Date(milliseconds); new Data(datestring); new Data(y, m, d, h, m, s, ms);   ## methods   date.toString() return  a time string date.valueOf() returns timestamp returns current timestamp Date.parse() returns a timestamp Date.UTC(y, m, d, h, m, s, ms) returns utc timestamp   # Globals   encodeURI() encode URI to %xx syntax encodeURIComponent encode every character including /?=+,# decodeURI   decodeURIComponent   isFinite()   isNaN   parseInt   parseFloat   Infinity       # Math   Math.random() // -> random number between 0 and 1
# String
String.substr(start, length)
String.substring(from, to)

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