【筆記】JavaScript編碼規範- 類型分配&強制轉換

標籤：javascript

執行強制類型轉換語句。

String

// bad <p>// => this.reviewScore = 9;</p>var A= this.reviewScore + '';// goodvar totalScore = '' + this.reviewScore;// badvar totalScore = '' + this.reviewScore + ' total score';// goodvar totalScore = this.reviewScore + ' total score';

使用parseInt對Numbers進行轉換，並帶一個進位作為參數

var A= '4';// badvar val = new Number(A);// badvar val = +A;// badvar val = A>> 0;// badvar val = parseInt(A);// goodvar val = Number(A);// goodvar val = parseInt(A, 10);

無論出於什麼原因，或許你做了一些”粗野”的事；或許parseInt成了你的瓶頸；或許考慮到效能，需要使用位元運算，都要用注釋說明你為什麼這麼做

// good/*** parseInt was the reason my code was slow.* Bitshifting the String to coerce it to a* Number made it a lot faster.*/var val = inputValue >> 0;

注意：當使用位元運算時，Numbers被視為64位值，但是位元運算總是返回32位整型(source)。對於整型值大於32位的進行位元運算將導致不可預見的行為。Discussion.最大的有符號32位整數是2,147,483,647

2147483647 >> 0 //=> 21474836472147483648 >> 0 //=> -21474836482147483649 >> 0 //=> -2147483647

Booleans:

var age = 0;// badvar hasAge = new Boolean(age);// goodvar hasAge = Boolean(age);// goodvar hasAge = !!age;

1:14 And God said,Let there be lights in the firmament of the heaven to divide the day from the night;and let them be for signs,and for seasons,and for days,and years:

【筆記】JavaScript編碼規範- 類型分配&強制轉換