> For the complete documentation index, see [llms.txt](https://jianghua-yjhs-organization.gitbook.io/in-depth-understanding-of-node.js-core-ideas-and/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jianghua-yjhs-organization.gitbook.io/in-depth-understanding-of-node.js-core-ideas-and/chapter14-5.md). # 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: ```js 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: ```js [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. #### Reference * --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation by asking a question. Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters: ``` GET https://jianghua-yjhs-organization.gitbook.io/in-depth-understanding-of-node.js-core-ideas-and/chapter14-5.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.