Browse
Log in / Register
Share
Automated validation tools can quickly identify JavaScript syntax errors, like problematic trailing commas, that break in Internet Explorer (IE), saving developers significant debugging time. This guide outlines a command-line method using Windows Script Host to parse files without browser testing. Catching these errors early in the development cycle is crucial for IE compatibility.
What is the core issue with Internet Explorer and JavaScript?
The core problem is that older versions of Microsoft Internet Explorer do not support trailing commas in arrays ([1, 2, ]) and object literals ({a: 1, b: 2, }). These final commas cause syntax errors that halt script execution in IE. While modern browsers ignore this syntax, it remains a common source of bugs for applications requiring legacy browser support.
How can you detect syntax errors from the command line?
You can use the Windows Scripting Host (WSH), a built-in feature on Windows XP and later, to check JavaScript syntax headlessly. The tool cscript.exe executes JScript (Microsoft's implementation of JavaScript) outside a browser. By creating a simple parser script, you can automate the detection of parsing errors across an entire codebase. This method is faster than initial browser testing.
To implement this, create a file named wsh-parser.js. The script should use the ActiveXObject("Scripting.FileSystemObject") to traverse directories and read .js files. The critical parsing function uses a technique to validate syntax without executing code:
new Function("return " + javaScriptCodeString + ";");
This line attempts to create a new function from the code string. If the string contains a syntax error, the new Function constructor will throw an exception, which your script can catch and report. This approach safely checks syntax by leveraging function declaration rather than execution.
How does this method compare to other validation tools? While tools like JSLint can also detect trailing commas, they often enforce a broader set of coding rules that may not align with your project's style guide. This can generate numerous warnings for issues you may not consider critical. The WSH parser method is purpose-built for one task: identifying code that will fail to parse in IE. It provides a fast, targeted check ideal for integration into a build process. Automated validators should be used alongside, but before, more comprehensive headless unit tests (e.g., JsUnit, RhinoUnit) and live browser testing frameworks like Selenium. Running the fast syntax check first allows developers to fix obvious errors immediately.
Integrating automated validation into your workflow. Establishing a sequence for quality checks improves efficiency. Start with automated syntax validators because they are fast and the errors are typically straightforward to fix. Once the code passes syntax checks, proceed to headless unit tests to verify logic. Finally, conduct live browser tests to ensure full compatibility. This layered approach prevents simple syntax errors from consuming time during complex testing phases. Based on our experience assessment, addressing parsing issues early streamlines the entire development and testing cycle.
