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[JavaScript] The difference between let and var definition variables in js

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Posted on 8/9/2017 5:25:50 PM | | |
javascrip{filter}t strict mode

When you first encounter the let keyword, there is a concept that you need to pay very, very attention to is "Javascrip{filtering}t strict mode", for example, the following code will run an error:



The error message reads:



The workaround is to add the "javascrip{filter}t strict mode" declaration to the file header:




For a single function
If you put "use strict" on the first line of the function body, the entire function runs in "strict mode".




Similarities and differences between let and var keywords

The declaration is not assigned, and the performance is the same



Using undeclared variables, the performance is different:



When repeatedly declaring the same variable, the behavior is different:



The scope of variables is different







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