#### 1. 强制转换： 1. Number(value) string, boolean --> Number(value) 特点：只能识别纯数字的字符串 true --> 1 false --> 0 ``` var a = "12"; var b = "true"; var c = true; var d = false; console.log(Number(a)); //12 console.log(Number(b)); //NaN console.log(Number(c)); //1 console.log(Number(d)); //0 ``` 2. string --> Number parseInt(), parseFloat() 3. other --> Boolean Boolean() 4. other --> String String() toString() #### 2. 自动转换： 发生在计算中：算术，比较，逻辑，三目，赋值 1. 只要一边为boolean，先将其转为number 2. 字符串和数字相加，转化为字符串 3. NaN与任何值计算都是NaN