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addChainableMethod.js
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addChainableMethod.js
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/*!
* Chai - addChainingMethod utility
* Copyright(c) 2012-2014 Jake Luer <jake@alogicalparadox.com>
* MIT Licensed
*/
/*!
* Module dependencies
*/
var transferFlags = require('./transferFlags');
var flag = require('./flag');
var proxify = require('./proxify');
/*!
* Module variables
*/
// Check whether `__proto__` is supported
var hasProtoSupport = '__proto__' in Object;
// Without `__proto__` support, this module will need to add properties to a function.
// However, some Function.prototype methods cannot be overwritten,
// and there seems no easy cross-platform way to detect them (@see chaijs/chai/issues/69).
var excludeNames = /^(?:length|name|arguments|caller)$/;
// Cache `Function` properties
var call = Function.prototype.call,
apply = Function.prototype.apply;
/**
* ### addChainableMethod (ctx, name, method, chainingBehavior)
*
* Adds a method to an object, such that the method can also be chained.
*
* utils.addChainableMethod(chai.Assertion.prototype, 'foo', function (str) {
* var obj = utils.flag(this, 'object');
* new chai.Assertion(obj).to.be.equal(str);
* });
*
* Can also be accessed directly from `chai.Assertion`.
*
* chai.Assertion.addChainableMethod('foo', fn, chainingBehavior);
*
* The result can then be used as both a method assertion, executing both `method` and
* `chainingBehavior`, or as a language chain, which only executes `chainingBehavior`.
*
* expect(fooStr).to.be.foo('bar');
* expect(fooStr).to.be.foo.equal('foo');
*
* @param {Object} ctx object to which the method is added
* @param {String} name of method to add
* @param {Function} method function to be used for `name`, when called
* @param {Function} chainingBehavior function to be called every time the property is accessed
* @namespace Utils
* @name addChainableMethod
* @api public
*/
module.exports = function (ctx, name, method, chainingBehavior) {
if (typeof chainingBehavior !== 'function') {
chainingBehavior = function () { };
}
var chainableBehavior = {
method: method
, chainingBehavior: chainingBehavior
};
// save the methods so we can overwrite them later, if we need to.
if (!ctx.__methods) {
ctx.__methods = {};
}
ctx.__methods[name] = chainableBehavior;
Object.defineProperty(ctx, name,
{ get: function () {
chainableBehavior.chainingBehavior.call(this);
var assert = function assert() {
var old_ssfi = flag(this, 'ssfi');
if (old_ssfi)
flag(this, 'ssfi', assert);
var result = chainableBehavior.method.apply(this, arguments);
return result === undefined ? this : result;
};
// Use `__proto__` if available
if (hasProtoSupport) {
// Inherit all properties from the object by replacing the `Function` prototype
var prototype = assert.__proto__ = Object.create(this);
// Restore the `call` and `apply` methods from `Function`
prototype.call = call;
prototype.apply = apply;
}
// Otherwise, redefine all properties (slow!)
else {
var asserterNames = Object.getOwnPropertyNames(ctx);
asserterNames.forEach(function (asserterName) {
if (!excludeNames.test(asserterName)) {
var pd = Object.getOwnPropertyDescriptor(ctx, asserterName);
Object.defineProperty(assert, asserterName, pd);
}
});
}
transferFlags(this, assert);
return proxify(assert);
}
, configurable: true
});
};