There’s a predefined Postfix template that allows you to type .log after a JavaScript expression or string and hit Tab to transform it to console.log().
You can also create a Live template (see Preferences | Editor | Live templates) that would expand into a code snippet once you type the selected abbreviation and hit Tab.
Update: there’s now also a plugin that allows you to add console.log with a shortcut: https://plugins.jetbrains.com/plugin/10986-console-log