use-isInstance.rst (1215B)
1 use-isInstance 2 ============== 3 4 Prefer ``.isInstance()`` in chrome scripts over the standard ``instanceof`` 5 operator for DOM interfaces, since the latter will return false when the object 6 is created from a different context. 7 8 These files are covered: 9 10 - ``*.sys.mjs`` 11 - ``*.xhtml`` with ``there.is.only.xul`` 12 - ``*.js`` with a heuristic 13 14 Since there is no straightforward way to detect chrome scripts, currently the 15 linter assumes that any script including the following words are chrome 16 privileged. This of course may not be sufficient and is open for change: 17 18 - ``ChromeUtils``, but not ``SpecialPowers.ChromeUtils`` 19 - ``BrowserTestUtils``, ``PlacesUtils`` 20 - ``document.createXULElement`` 21 - ``loader.lazyRequireGetter`` 22 - ``Services.foo``, but not ``SpecialPowers.Services.foo`` 23 24 Examples of incorrect code for this rule: 25 ----------------------------------------- 26 27 .. code-block:: js 28 29 node instanceof Node 30 text instanceof win.Text 31 target instanceof this.contentWindow.HTMLAudioElement 32 33 Examples of correct code for this rule: 34 --------------------------------------- 35 36 .. code-block:: js 37 38 Node.isInstance(node) 39 win.Text.isInstance(text) 40 this.contentWindow.HTMLAudioElement.isInstance(target)