In JavaScript, function declaration takes precedence over instance analysis of variable declaration.

Copy codeThe Code is as follows: var a; // declare a variable with the identifier
Function a () {// declare a function. The identifier is.
}
Alert (typeof );

"Function" is displayed, that is, the priority of a function is higher than that of var.
Some people think this is the reason for sequential code execution, that is, a is overwritten by the funcion executed later. Okay. change them.Copy codeThe Code is as follows: function (){
}
Var;
Alert (typeof );

The result still shows "function" instead of "undefined ". That is, function declaration takes precedence over variable declaration.
We make a slight modification to the code and assign values when declaring.Copy codeThe Code is as follows: function (){
}
Var a = 1; // note that
Alert (typeof );

"Number" is displayed but not "function", which is equivalentCopy codeThe Code is as follows: function (){
}
Var;
A = 1; // note that
Alert (typeof );

Split "var a = 1" into two steps. A is re-assigned, which is the final value.