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Below are the major differences between undeclared(not defined) and undefined variables,
| undeclared | undefined |
| ------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------- |
| These variables do not exist in a program and are not declared | These variables declared in the program but have not assigned any value |
| If you try to read the value of an undeclared variable, then a runtime error is encountered | If you try to read the value of an undefined variable, an undefined value is returned. |
1var a;
2
3a; // yields undefined
4
5b; // Throws runtime error like "Uncaught ReferenceError: b is not defined"This can be confusing, because it says not defined instead of not declared (Chrome)
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JavaScript Coding Exercise 82
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