JS-二 _JavaScript

JS-2

JS还是有些奇怪的东西的也不知道怎么去看源码才能知道这奇怪的来源

isNaN(5/0); // false
isNaN(0/0); // true

5/0; // infinity

0.1 + 0.2; // 0.30000000000000004

Math.round((0.1+0.2)*100)/100; // 0.3

JS的Object是基于key-value的map机制实现的，并且往往是string-object的搭配

JS可以用Object作为key，但是也是转换为object.toString来判断key值

var obj = {};
var otherObj = {
    name: "other"
};

var map = {};
map[obj] = 'first';
map[otherObj] = 'second';

map[obj]; // This is 'second'.

// Recall that object keys are strings. The string
// generated by an object is '[object Object]' by default.
// So, obj and otherObj have the same key; 
// map[obj] and map[otherObj] are therefore equivalent.

console.log(obj.toString);
console.log(otherObj.toString);