From jQuery JavaScript Library

Spacing

Use tabs to indent your code.

Be sure to use liberal spacing in your code.

   // No:
   if(blah==="foo"){
     foo("bar","baz",{zoo:1});
   }
   
   // Yes:
   if ( blah === "foo" ) {
     foo( "bar", "baz", {zoo: 1} );
   }

Equality

Strict equality checks (===) should be used in favor of == wherever possible.

Blocks

Braces should always be used on blocks.

   // NO:
   if ( true )
      blah();
   
   // YES:
   if ( true ) {
      blah();
   }

Don't put statements on the same line as a conditional.

   // NO:
   if ( true ) return;
   if ( true ) blah();
   
   // YES:
   if ( true ) {
      return;
   }
   
   if ( true ) {
      blah();
   }

Don't use ternary operators instead of if/else statements.

Don't use object && object.method() instead of if/else statements (except in conditionals).

Type Checks

• String: typeof object === "string"
• Number: typeof object === "number"
• Boolean: typeof object === "boolean"
• Object: typeof object === "object"
• Function: jQuery.isFunction(object)
• Array: jQuery.isArray(object)
• Element: object.nodeType
• null: object === null
• null or undefined: object == null
• undefined:
  • Global Variables: typeof variable === "undefined"
  • Local Variables: variable === undefined
  • Properties: object.prop === undefined

RegExp

All RegExp operations should be done using .test() and .exec(). "string".match() is no longer used.

Nodes

.nodeName should always be used in favor of .tagName.

.nodeType should be used to determine the classification of a node (not .nodeName).

Don't attach expandos to nodes - only attach data using .data().