Why do JavaScript statements have to end with a semicolon ";"? -

while writing js code front-end business project, wondered why have end js statements semicolon ?

so main use of semicolon in javascript ?

thanks answers.

';' mean end of code line , ';' can write js code in 1 line @ following example

alert("a")alert("b"); //this return error uncaught syntaxerror 

but

alert("a");alert("b");//this work fine