type

Author: wang-jun-coder

Note/type/type.js

@@ -16,12 +16,193 @@
 
 (function() {
 
-	// 实际上 1. Number(1) 的原型 与 Number 对应的原型相同
+	// instanceof 无法判断基本类型
 	console.log(1 instanceof Number);	
 	console.log(Number(1) instanceof Number);
 	console.log(new Number(1) instanceof Number); // new 使得对象为 Number 的实例
-	console.log((1).prototype == Number.prototype && (Number(1)).prototype == Number.prototype);
 	// false false true
 
+	// __proto__ 是一组 getter/setter 函数, 用于访问对象内部的原型
+	// prototype 是对象继承属性方法的来源, 一般为了避免修改原型导致影响其他对象, 原型一般 new 实例
+	console.log((1).__proto__ == Number.prototype && (Number(1)).__proto__.__proto__ == Number.prototype.__proto__);// true
+
+	function Person(name) {
+		this.name = name;
+	}
+	const p = new Person('somebody');
+	console.log(p instanceof Person); // true
+	console.log(p.__proto__ === Person.prototype); // true
+	console.log(p.__proto__.__proto__ === Object.prototype); // true
+
+	// 模拟实现 instanceof, 实际上就是遍历对比原型
+	function isInstanceof(obj, p) {
+		if (typeof obj !== 'object') return false;
+		while(obj) {
+			if (p.prototype === obj.__proto__ ) return true;
+			obj = obj.__proto__;
+		}
+		return false;
+	}
+	console.log(isInstanceof(p, Person)); // true
+
+}); //();
+
+(function(){
+	// constructor 判断
+	console.log((1).constructor); // [Function: Number]
+	console.log('1'.constructor); // [Function: String]
+	console.log((true).constructor); // [Function: Boolean]
+	console.log(Symbol('s').constructor); // [Function: Symbol]
+	// console.log(null.constructor); // TypeError: Cannot read property 'constructor' of null
+	// console.log(undefined.constructor); // TypeError: Cannot read property 'constructor' of undefined
+	console.log({}.constructor); // [Function: Object]
+	console.log([].constructor); // [Function: Array]
+	console.log(new Set().constructor); // [Function: Set]
+	console.log(new Date().constructor); // [Function: Date]
+	console.log((() => 1).constructor);	// [Function: Function]
+
+	function Person(){}
+	const p = new Person();
+	console.log(p.constructor); // [Function: Person]
+
+}); //();
+
+(function(){
+
+	const toString = Object.prototype.toString;
+
+	console.log(toString.call(1)); // [object Number]
+	console.log(toString.call('1')); // [object String]
+	console.log(toString.call(true)); // [object Boolean]
+	console.log(toString.call(Symbol('s'))); // [object Symbol]
+	console.log(toString.call(null)); // [object Null]
+	console.log(toString.call(undefined)); // [object Undefined]
+	console.log(toString.call({})); // [object Object]
+	console.log(toString.call([])); // [object Array]
+	console.log(toString.call(new Set())); // [object Set]
+	console.log(toString.call(new Date())); // [object Date]
+	console.log(toString.call((()=>1))); // [object Function]
+	
+	function Person(){}
+	const p = new Person();
+	console.log(toString.call(p)); // [object Object]
+});//();
+
+
+(function(){
+	// number + 
+	console.log(1 + '1');	// 11
+	console.log(1 + true);	// 2
+	console.log(1 + false);	// 1
+	console.log(1 + null);	// 1
+	console.log(1 + undefined); // NaN
+
+	console.log('-------------------------');
+
+	// string + => string
+	console.log('1' + '1');	// 11
+	console.log('1' + true);	// 1true
+	console.log('1' + false);	// 1false
+	console.log('1' + null);	// 1null
+	console.log('1' + undefined); // 1undefined
+
+	console.log('-------------------------');	
+
+	// number -
+	console.log(1 - '1');	// 0
+	console.log(1 - true);	// 0
+	console.log(1 - false);	// 1
+	console.log(1 - null);	// 1
+	console.log(1 - undefined); // NaN
+
+	console.log('-------------------------');
+
+	// string - 
+	console.log('1' - '1');		// 0
+	console.log('1' - true);	// 0
+	console.log('1' - false);	// 1
+	console.log('1' - null);	// 1
+	console.log('1' - undefined); // NaN
+
+	console.log('-------------------------');
+
+	// other -
+	console.log(true - true); // 0
+	console.log(true - false); // 1
+	console.log(true - null); // 1
+	console.log(true - undefined); // NaN
+
+	console.log('-------------------------');
+	
+	// 复杂类型
+	const a = {
+		valueOf(){
+			return 1;
+		}
+	};
+	const b = {
+		toString() {
+			return '2';
+		}
+	};
+	const c = {
+		valueOf(){
+			return 3;
+		},
+		toString() {
+			return '4';
+		}	
+	}
+	console.log(1 + a);	// 2; -> a.valueOf
+	console.log(1 + b);	// 12; -> b.toString
+	console.log(1 + c);	// 4;	-> c.valueOf
+	console.log("1" + a);	// 11; 
+	console.log("1" + b);	// 12;
+	console.log("1" + c);	// 13;
+
+	console.log(1 - a);	// 0
+	console.log(1 - b);	// -1	
+	console.log(1 - c);	// -2
+	console.log("1" - a); // 0
+	console.log("1" - b); // -1
+	console.log("1" - c); // -2
+
+});// ();
+
+(function(){
+
+	console.log([10] == 10); 	// true; [10] == 10 => '10' == 10 => true
+	console.log('10' == 10);
+	console.log([] == 0); 		// true; [] == 0 => '' == 0 => Number('') == 0 => true
+	console.log(true == 1); 	// true; true == 1 => Number(true) == 1 => true
+	console.log([] == false);	// true; [] == false => '' == false => '' == 0 => true
+	console.log(![] == false);	// true; ![] == false => false == false => true
+	console.log('' == 0);
+	console.log('' == false);
+	console.log(null == false); // false; null == false =>  null == 0 => false
+	console.log(!null == true); // true; !null == true => true == true => true;
+	console.log(null == undefined); // true;
+
+
+	console.log(null === undefined); 	// false;
+	console.log(NaN === NaN); 			// false;
+	console.log(1 === 1);					// true;
+	console.log(+0 === -0);				// true;
+	console.log(undefined === undefined); // true;
+	console.log(null === null); 		// true;
+	console.log('aaab' === 'aaab');		// true;
+	console.log(Symbol.for('1') === Symbol.for('1')); // true;
+	console.log([] === []); // false;
+	let a = b = [];
+	console.log(a === b); // true;
+
+	// 注意:
+	console.log([] == 0); // true;
+	console.log([] == []); // false; // 两侧类型相同,均为 object, 相当于 [] === []
+
+
+})();
+
+
+
 
-})();