First, the error
1, a syntax error
Error, prompted, it is easy to solve.
2, logic errors
Not easy to find
Second, the debug mode
1, alert () mode
2, console.log () / console.error () mode
3, breakpoint debugging
Breakpoint debugging refers to himself in a row setup a breakpoint, the debugger, the program will stop running to the line, then you can down step by step debugging, the debugging process can see the current values of individual variables, error then the error debugging to the line of code that is an error, stop.
Commissioning steps:
Browser, press F12 -> sources -> find the file needed to debug -> Set a breakpoint in a row the program
Figure:
4, debugging related operations
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- Watch: monitoring, it can be monitored by changes in the value of the variable Watch, very common.
- F10: single-step program execution, allowing the implementation of the program line by line, this time to observe the changes in the value of the watch variables.
- F8: skip to the next breakpoint, if there is no break back, and the end of program execution.
Tips: watch variables, do not watch expressions, because monitoring the expression, the expression will be executed