Porting code to ES5 standards mode scripts

ES5 standards mode catches errors that compatibility mode allows.

Things to watch for when porting code from existing scripts to new scoped scripts using ES5 standards mode.

ECMAScript5 evaluates the term new Boolean(false) to true. In compatibility mode, it evaluated to false.

ECMAScript5 throws an EcmaError when a non-existent property is referenced. In compatibility mode no error was thrown.

ECMAScript5 throws an EcmaError when a non-existent function is called. In compatibility mode, no error was thrown.

ECMAScript5 correctly handles new lines. In the past, a newline character after a comment was recognized, which is wrong. In this example, in compatibility mode, all three functions are called. In ECMAScript5, only the first function is called.

var expr = doFoo();  // do foo
           doBar();  // do bar 
           finish();   // all done
 eval(expr);

ECMAScript5 correctly handles postfix increment and decrement. In this example, in compatibility mode, the variable x gets the incremented value, which is wrong.

var x = gr.limit++;