javascript類型的動態轉換

雖然知道js的類型明確指定，可是在使用中變換類型，竟然也是能夠的，例如

<script>

var a, b, c;

a = 10;

b = "astring";

c = [5, 2, 4, 6];

a = a + 5;

alert(a);//15

b = b.concat("additional words", "ending");

alert(b);//"astringadditional wordsending

c = c.map(function(e){return e*2;});//10,4,8,12

alert(c);

a = b;

alert(a);//"astringadditional wordsending

b = c.length;

alert(b);//4

c = c.join("/");

alert(c);//10/4/8/12

</script>

但我以爲，知道有這個功能就能夠了，爲了節省個變量名，這麼變來變去，玩死本身，得不償失。