Node.js pitfalls

JavaScript Pitfalls

Weak Typing

  • To check if an object does not exist, using if(!obj) will also mistake '', 0, or false as non-existent. The correct way to do this is more complex: see reference.

  • String concatenation will usually automatically convert to a string, but if the first two happen to be able to be converted to numbers, it will add them as numbers. For example:

var a = 1,b = 'b',c = 10;
var s1 = a + c + b;
var s2 = '' + a + c + b;
console.log(s1); //"11b"
console.log(s2); //"110b"

To be safe: use Number conversion.

This Pointer

  • Normally, when called, this is the global object of the window, for example in a browser it is the window object.

  • .call and .apply methods can change the value of this.

  • In a prototype function, this points to the instance object created by the class.

Sorting

The sort() method of JavaScript's Array is used for sorting, but the sorting result may surprise you:

[10, 20, 1, 2].sort(); // [1, 10, 2, 20]

This is because the sort() method of Array defaults to converting all elements to String before sorting, so '10' is ranked ahead of '2' because the character '1' has a smaller ASCII code than the character '2'.

If you don't know the default sorting rules of the sort() method, sorting numbers directly will definitely get you into trouble! Fortunately, the sort() method is also a higher-order function, which can receive a comparison function to implement custom sorting.

Asynchronous Processing

  • Forgetting to return when handling errors.

  • Improper handling in an asynchronous method may trigger the callback multiple times, or not trigger any callback at all. Careful handling of the logical flow is required.

Scientific Calculation

  • The internal implementation of the Number object in the v8 engine of JavaScript has only two types: smi (small integers) and double. Node.js does not have float at all! If you use float, be aware of the loss of precision.

  • Bitwise operations are only supported up to 32 bits in JavaScript. For more than 32 bits, you need to simulate with big numbers. https://github.com/justmoon/node-bignum

Reference

  • http://www.ruanyifeng.com/blog/2011/05/how_to_judge_the_existence_of_a_global_object_in_javascript.html

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