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/*!
* Chai - overwriteProperty utility
* Copyright(c) 2012-2014 Jake Luer <jake@alogicalparadox.com>
* MIT Licensed
*/
var chai = require('../../chai');
var flag = require('./flag');
var isProxyEnabled = require('./isProxyEnabled');
var transferFlags = require('./transferFlags');
/**
* ### .overwriteProperty(ctx, name, fn)
*
* Overwrites an already existing property getter and provides
* access to previous value. Must return function to use as getter.
*
* utils.overwriteProperty(chai.Assertion.prototype, 'ok', function (_super) {
* return function () {
* var obj = utils.flag(this, 'object');
* if (obj instanceof Foo) {
* new chai.Assertion(obj.name).to.equal('bar');
* } else {
* _super.call(this);
* }
* }
* });
*
*
* Can also be accessed directly from `chai.Assertion`.
*
* chai.Assertion.overwriteProperty('foo', fn);
*
* Then can be used as any other assertion.
*
* expect(myFoo).to.be.ok;
*
* @param {Object} ctx object whose property is to be overwritten
* @param {String} name of property to overwrite
* @param {Function} getter function that returns a getter function to be used for name
* @namespace Utils
* @name overwriteProperty
* @api public
*/
module.exports = function overwriteProperty(ctx, name, getter) {
var _get = Object.getOwnPropertyDescriptor(ctx, name)
, _super = function () {};
if (_get && 'function' === typeof _get.get)
_super = _get.get
Object.defineProperty(ctx, name,
{ get: function overwritingPropertyGetter() {
// Setting the `ssfi` flag to `overwritingPropertyGetter` causes this
// function to be the starting point for removing implementation frames
// from the stack trace of a failed assertion.
//
// However, we only want to use this function as the starting point if
// the `lockSsfi` flag isn't set and proxy protection is disabled.
//
// If the `lockSsfi` flag is set, then either this assertion has been
// overwritten by another assertion, or this assertion is being invoked
// from inside of another assertion. In the first case, the `ssfi` flag
// has already been set by the overwriting assertion. In the second
// case, the `ssfi` flag has already been set by the outer assertion.
//
// If proxy protection is enabled, then the `ssfi` flag has already been
// set by the proxy getter.
if (!isProxyEnabled() && !flag(this, 'lockSsfi')) {
flag(this, 'ssfi', overwritingPropertyGetter);
}
// Setting the `lockSsfi` flag to `true` prevents the overwritten
// assertion from changing the `ssfi` flag. By this point, the `ssfi`
// flag is already set to the correct starting point for this assertion.
var origLockSsfi = flag(this, 'lockSsfi');
flag(this, 'lockSsfi', true);
var result = getter(_super).call(this);
flag(this, 'lockSsfi', origLockSsfi);
if (result !== undefined) {
return result;
}
var newAssertion = new chai.Assertion();
transferFlags(this, newAssertion);
return newAssertion;
}
, configurable: true
});
};
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