Local variables in JavaScript are function-scoped (unlike, for instance, in Java, which uses block scope), and can be redeclared an arbitrary number of times. If a variable is declared twice in different blocks, however, this can confuse readers, since the declarations look like they refer to different variables.

If the two declarations logically refer to the same variable, replace them with a single declaration at the beginning of the block. If they do not, rename one of the variables to distinguish it from the other.

In the following code snippet, both declarations for value declare the same local variable, although their uses are independent.

D. Crockford, JavaScript: The Good Parts, Section 4.9. O'Reilly, 2008.