Having trouble with code behaving differently than expected in Chrome's debugger

I've come across a peculiar issue in my TypeScript project (an Angular application). Here's the code snippet that's causing trouble:

const idx = myclone.findIndex(x => x.id === action.id);
const hasVal = idx>-1; // for some reason, Chrome debugger is skipping this line
if (idx>-1) { // despite idx===0, this condition always turns out to be false
  myclone[idx].upload = action.status;
  return {
    ...state,
    ProgressFiles: myclone,
  };
} else {
  return state; // strangely enough, this block is executed even when idx > -1
}

It seems like there might be an issue with line 2 (which was added for debugging purposes) and line 3. However, I can't seem to pinpoint what exactly is wrong. The code appears to be correct to me, but the Chrome debugger is skipping over line 2 and incorrectly evaluating the if statement as false, despite idx being equal to 0. Any ideas on what could be going awry here?

Answer №1

Quick tip: To troubleshoot your code, insert a debugger; statement after Line 2.

Insight: The issue you are experiencing is likely due to small errors in the source maps generated by the specific version of Angular you are using.

Source maps serve as guides (often seen as JavaScript comments) that certain browsers and integrated development environments can interpret. These guides establish connections between the final built file (the code that actually runs in the browser) and the original code files (e.g. .ts).

As you may be aware, TypeScript does not directly execute in the browser environment; therefore, it undergoes transpilation and additional processes. In development mode, Angular automatically generates a source map to facilitate debugging.

When the debugger analyzes the compiled JS code alongside the source maps, it aligns the executing lines with the corresponding lines in the TypeScript files. While there might be some discrepancies (such as missing or added lines), the debugger should generally assist in achieving your debugging objectives.

In any case, integrating a debugger statement ensures precise breakpoints during the debugging process.

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