1 any—->number

  1. console.log(Number("3")); // 3
  2. console.log(Number(true)); // 1，false为0
  3. console.log(Number(null)); //0
  4. console.log(Number(undefined));//NaN
  5. console.log(Number("hello"));//NaN

2 any to boolean

  1. 0--->false,其他数字为true
  2. ""--->false,其他情况为true
  3. console.log(Boolean(null));//false
  4. console.log(Boolean(undefined));//false
  5. console.log(Boolean(NaN));//false

3 any to string

  1. String();
  2. toString();
  3. +"";