Learn ECMAScript - Second Edition

Automatic semicolon insertion in JavaScript

The ECMAScript Language specification (http://www.ecma-international.org/ecma-262/5.1/#sec-7.9) states that:

"Certain ECMAScript statements must be terminated with semicolons. Such semicolons may always appear explicitly in the source text"

But the spec also says:

"For convenience, however, such semicolons may be omitted from the source text in certain situations."

Therefore, the specification states that JavaScript is able to handle automatic semicolon insertion by its own judgment. However, it is extremely error-prone in some cases and not intuitive at all.

Consider this example:

var a = 1 var b = 2 var c = 3

JavaScript automatically inserts semicolon to make code look like:

var a = 1;var b