Today, for the first time, a const-defined variable was encountered, and the article was collated with relevant data. The main content is: JS in three ways to define the variable const, VAR, let the difference.
Variables defined by 1.const cannot be modified and must be initialized.
2.var defined variables can be modified, if not initialized will output undefined, will not error.
1 var a = 1;2//var a;//will not error 3 Console.log (' Out of function var definition a: ' + a ');//Can output a=14 function change () {5 A = 4;6 Console.log (' var within function ' definition a : ' + a);//Can output a=47} 8 Change (), 9 console.log (' function call after Var definition A is the function of the internal modified value: ' + a);//Can output a=4
3.let is a block-level scope, and after the function is defined with let, there is no effect on the outside of the function.
1 Let C = 3;2 console.log (' Out of function let ' definition C: ' + C ');//Output c=33 function change () {4 let c = 6;5 console.log (' in function let definition C: ' + C);//Output c=6 6} 7 change (); 8 Console.log (' A let definition after a function call is not affected by the internal definition of the function: ' + C ');//Output c=3
If there is any mistake, please correct me!
Const,var,let Differences in JS