JS daily question (10)

js A daily topic

let a = a , What problems occur during operation ？ Why? ？
** There are two stages ：
1. In the precompile phase , take let The declared variables are put into the temporary deadband TDZ in TDZ = [a].
2. When let After the declaration statement , The end here refers to , When let a = a After execution , Will be able to a from TDZ Took out . however let a = a When it comes to execution , Assigned on the right a still TDZ in , So wrong reporting . That is, the error of using without declaration .
therefore , We are using let When declaring variables , Remember to declare before using .
**
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