In the image above, I tried setting breakpoints on every line from line 437 to line 443. However, I cannot set breakpoints on lines 439 and 440. When the function runs, the breakpoints on lines 437, 438, 441, and 442 are ignored. Chrome breaks on line 443. This means that I cannot do some debugging before the first conditional runs.
When I click on lines 439 or 440, the breakpoint appears for half a second and jumps to line 443.
Is this a bug or am I missing something? How do I set a breakpoint at or before line 439?
If you are using js minification and sourcemaps, ensure that they are up to date with your source code.
This recently became an issue for me, running System.js and Babel, and with plain ES6 transpiling, I haven't gotten to minifying/mapping yet. A workaround seems to be to add your breakpoint to the !transpiled file, a matching breakpoint will automagically appear in the corresponding line in the raw file.
I have same problem in chrome dev tool source panel snippets when I write some codes to test my idea.
Only way for me worked is close dev tool panel and refresh page then reopen
This problem happened after I modified codes in debug mode
来源：https://stackoverflow.com/questions/35278193/chrome-devtools-wont-let-me-set-breakpoints-on-certain-lines