(Sourced from here.)
Square bracket notation allows the use of characters that can’t be used with dot notation:
var foo = myForm.foo[]; // incorrect syntax var foo = myForm["foo[]"]; // correct syntax
including non-ASCII (UTF-8) characters, as in myForm["ダ"]
(more examples).
Secondly, square bracket notation is useful when dealing with
property names which vary in a predictable way:
for (var i = 0; i < 10; i++) { someFunction(myForm["myControlNumber" + i]); }
Roundup:
- Dot notation is faster to write and clearer to read.
- Square bracket notation allows access to properties containing
special characters and selection of
properties using variables
Another example of characters that can’t be used with dot notation is property names that themselves contain a dot.
For example a json response could contain a property called bar.Baz
.
var foo = myResponse.bar.Baz; // incorrect syntax
var foo = myResponse["bar.Baz"]; // correct syntax