Javascript -- Number

typeof Infinity ==> returns "number";

typeof NaN      ==> returns "number"   (Nan is short for Not a number)

<script>
    var x = 100 / "Hoabart";
    var y = 100 / 10;
    var z = 100 / "20";
    alert(x);    // ==>NaN     isNaN(x) 可以判断x是否为NaN类型
    alert(y);    // ==>10
    alert(z);    // ==>5
</script>

*toFixed(): returns a string, with the number written with a specified number of decimals

*toPrecision(): returns a string, with a number written with a specified length

 

Converting Variables to Numbers

　　*Number()

<script>
  var x = true;
  Number(x);       //returns 1
  var y = false;
  Number(y);       //returns 0
  var z = "10";
  Number(z);       //returns 10
  var i = "10 20";
  Number(i);       //returns NaN
  var j = new Date();
  Number(j);       //returns 2415345723970
</script>

 

　　*parseInt()

<script>
  parseFloat("10");           //returns 10
  parseFloat("10.33");       //returns 10
  parseFloat("10 20 30");   //returns 10
  parseFloat("10 years");   //returns 10
  parseFloat("years 10");   //returns NaN
</script>

　　*parseFloat()

<script>
  parseFloat("10");           //returns 10
  parseFloat("10.33");       //returns 10.33
  parseFloat("10 20 30");   //returns 10
  parseFloat("10 years");   //returns 10
  parseFloat("years 10");   //returns NaN
</script>