4-引用值初识

Array

var arr = [1, 2, 3, 4, 5, 6];
for (var i = 0; i < arr.length; i++){
  console.log(arr[i]);
}
arr[1] = 3;

Object对象

var person = {
  name: "liquan"m
  age: 18,
  hobby: ["sing", "jump", "rap"]
};

Typeof

console.log( typeof(123) ); // number
console.log( typeof({}) );  // object
console.log( typeof([]));   // object
console.log( typeof(null)); // object 
console.log( typeof(undefined)); // undefined
console.log( typeof(function(){}))// function
console.log( a ); // referenceError a is undefined
console.log( typeof(a) ); // undefined;
console.log( typeof(typeof(undefined))); //string
// {} 与 [] 都属于 object

null为啥为object

是bug，cpp用int代表js的类型，null是0开头，object开头，所以null返回object。属于历史遗留问题，es6有人提过要改null，但是被否决了