With the emergence of rich Web front-end applications, developers have to re-examine and pay attention to the capabilities and use of the JavaScript language, abandoning the past model of simply "copying/pasting" common scripts to complete simple front-end tasks. The JavaScript language itself is a weakly typed scripting language with looser restrictions than the C++ or Java language. All function-centered functional programming ideas also provide developers with more flexible syntax implementations. However, while this flexibility brings efficiency, it also becomes a nightmare for novice or inexperienced JavaScript developers. Different coding styles and erroneous code behaviors have seriously affected the readability and stability of the overall code, and have become one of the most common problems in Web projects.
Therefore, we need an effective JavaScript code quality tool so that we can promptly discover and correct problems hidden in JavaScript code and ensure the quality of code delivery. As a flexible and effective JavaScript code quality inspection tool, JSLint allows users to specify coding style conventions that meet their specific application development needs, making the entire project unified in style. This "rules" (options)-driven way of working makes JSLint applicable for different code detection needs. This article will first introduce readers to the basic concepts and functions of JSLint, explain its rule-based working method, and then illustrate its basic usage through an example. Finally, it will introduce how to integrate JSLint into the application process of Ant and Eclipse to demonstrate all aspects. How to use JSLint in daily development tasks.
What is JSLint
As a young language with flexible syntax and relatively loose format requirements, JavaScript has confusing code formats and incorrect use of certain language features, which often results in the final delivered product containing many unforeseen errors caused by coding style conventions. Behaviors or errors. If such habitual problems are not pointed out and corrected in time, they will often recur during the iteration process of the project, seriously affecting the stability and security of Web products. JSLint is a tool created by Douglas Crockford to solve such problems. In addition to pointing out these unreasonable conventions, JSLint can also mark structural problems. Although JSLint cannot guarantee that the code logic is correct, it can help find errors and teach developers some good coding practices. It is worth mentioning that the JSLint tool itself is also a piece of JavaScript code. It is a JavaScript script that checks the quality of JavaScript code. JSLint's quality inspection of JavaScript scripts mainly includes the following aspects:
• Detect syntax errors: For example, incorrect pairing of curly brackets "{}".
•Variable definition specifications: such as detection of undefined variables.
•Code format specifications: For example, the missing semicolon at the end of the sentence.
• Usage detection of crappy language features: usage restrictions such as eval and with.
The version update of JSLint has been active. As of the time of writing this article, the latest version of JSLint was released on 2010-10-10. Many mainstream code editors provide good extended support for JSLint, including Eclipse, VS2008, and so on.
Currently, there are many JavaScript code detection tools with similar functions to JSLint, including: YUI Test, Firebug, MS Script Debugger, CompanionJS, etc. Most of them exist in the form of browser plug-ins in the client browser to run JavaScript. The important difference between JSLint and these tools is that it pays more attention to the detection and debugging of static code formats, which is exactly what is needed and advocated for continuous construction in the current hot agile development.
Understand JSLint rules
The core principle of JSLint's code quality inspection lies in the set of rules set by the user. The rule set provided by JSLint by default contains the development styles that Web developers have accumulated over the years and consider them to be bad. We can choose to build a specific set of rules according to the needs of our own projects. JSLint will scan JavaScript scripts based on it and give corresponding problem description information. Rules are in the form of multiple sets of key-value pairs: [param:option], with the rule name as the key and whether the rule is called or not as the value. For example, the rule: "plusplus:true" does not allow the ++ and -- operators to appear, and "undef:true" does not allow the use of undefined variables.
Since the JSLint tool is essentially an ordinary JS script, its operation naturally relies on a JS runtime engine. After being loaded by the engine, it will generate a global JSLint function object in memory. This function object requires two inputs: source and options, the former is used to specify the string or string array generated after the script file to be detected is parsed, and the latter represents user-defined rule options. If options is empty, JSLint uses its default rules to scan and detect the source.
The entire detection process is an execution process of the JSLINT (source, options) function contained in the script. When the specified source script passes the detection under the options condition, JSLint returns true, otherwise it returns false, and at this time, detailed error information can be obtained through the JSLINT.errors object. Figure 1 shows the entire working process of JSLint.
Figure 1. Schematic diagram of JSLint working process
As shown in the figure, there are three ways to configure a rule set:
1. Modify the default rules directly by modifying the JSLint.js source code.
2. When the JSLint function is running, set the options parameter at the same time and dynamically change its rule options (first overwrite). This method is suitable for using the same set of custom rules for batch js files.
3. Add special rules (second overwrite) applicable to the code of a single js file by adding annotation type rules to the header of the js file to be detected. This method is suitable for setting specific detection rules for different js files, and is usually used to introduce some global variables in the file.