dom interceptor

• Background
• API

See the NPM module.

## Background

This library is designed for use with AngularHintDom, a runtime hinting tool that depends on detecting manipulation of the DOM in AngularJS applications to warn developers about best practices. The goal of this library is to explore different ways of 'intercepting' or patching DOM APIs in order to provide this hinting.

To provide this service, the library creates a main manipulationListener that is used by AngularHintDom. This listener is the interceptor that listens for use of certain DOM APIs.

Previously this library contained other methods for patching individual element properties and using proxies that are not used by the current manipulationListener. These methods were developed as part of an exploration of how to effectively listen for DOM manipulation.

Especially, the library aims to detect the use of methods such as:

• retrieval methods such as document.getElementById()
• element.remove
• element.insertBefore
• element.appendChild

Originally, other manipulative methods like element.innerHTML and element.parentElement were also identified as goal methods for the overall manipulationListener to detect. However, detecting these DOM APIs in certain browsers requires patching of individual elements (Firefox attaches properties like .innerHTML to Element.prototype so patching get/set properties of the prototypes would be sufficient in that browser). In an earlier iteration, methods patchExistingElements() and patchElementProperties() were implemented to fill this need. However, for the best effort goal of detecting DOM manipulation, patching individual elements was deemed too heavy-handed, dangerous, and costly in terms of performance. For example, some browsers such as Safari do not allow the patching of element properties. Moreover, these patched elements do not have the same behavior as unpatched elements.

A better solution than patchExistingElements() or patchElementProperties() for providing this interception on the level of individual elements is to use proxies. In one iteration, the method patchAccess() used the harmony-reflect library to provide this service.

However, proxies are still considered experimental javascript. In Chrome for instance this javascript feature can only be enabled by setting the flag chrome://flags/#enable-javascript-harmony. Hence, these features are not used be the current manipulationListener. Instead, the manipulationListener provides a 'best-effort' detection of the majority of DOM API calls by patching functions on the prototypes of Element, Node, and Document.

## API

####addManipulationListener

#####Use as: addManipulationListener(newListener)

Add a listener - a function - that will be fired when use of DOM APIs is detected.

####Example

var domInterceptor = require('dom-interceptor');
var listenerFunction = function(message) {
  console.log(message);
};
//Will console.log the given message when manipulation is detected
domInterceptor.addManipulationListener(listenerFunction);

####Params Param | Type | Description --- | --- | --- newListener | function | A function that will be triggered when use of DOM APIs is detected

####enableLineNumbers

#####Use as: enableLineNumbers(stackTraceLocation)

Enable the listener message passed to the given listener to include the line number of the call that manipulated the DOM. A stackTraceLocation is required in order to pick a line from the stack trace that is not within the domInterceptor code.

####Example

var domInterceptor = require('dom-interceptor');
domInterceptor.enableLineNumbers(3);

####Params Param | Type | Description --- | --- | --- stackTraceLocation | number | The line of the stack trace that is of interest to the user

####patchOnePrototype

#####Use as: patchOnePrototype(type, typeName)

Patch all functions on a given type.prototype to trigger the manipulationListener when called.

####Example

var domInterceptor = require('dom-interceptor');
domInterceptor.patchOnePrototype(Document, 'Document');
//Triggers the manipulationListener
document.getElementById('foo');

####Params Param | Type | Description --- | --- | --- type| function | A function whose prototype should be patched. typeName | String | The string name of the function whose prototype should be patched

####removeManipulationListener

#####Use as: removeManipulationListener()

Remove the manipulationListener.

####Example

var domInterceptor = require('dom-interceptor');
var listenerFunction = function(message) {
  console.log(message);
};
//Will console.log the given message when manipulation is detected
domInterceptor.addManipulationListener(listenerFunction);
//triggers console.log
document.getElementById('foo');

domInterceptor.removeManipulationListener();
//does not trigger console.log
document.getElementById('foo');

####unpatchOnePrototype

#####Use as: unpatchOnePrototype(type, typeName)

Unpatch all functions on a given type.prototype that had been patched to trigger the manipulationListener.

####Example

var domInterceptor = require('dom-interceptor');
domInterceptor.patchOnePrototype(Document, 'Document');
//Triggers the manipulationListener
document.getElementById('foo');
domInterceptor.unpatchOnePrototype(Document, 'Document');
//Does not trigger the manipulationListener
document.getElementById('foo');

####Params Param | Type | Description --- | --- | --- type| function | A function whose prototype should be unpatched. typeName | String | The string name of the function whose prototype should be unpatched

License

Apache 2.0