can-map.js
function () {
			this._computedAttrs = Object.create(null);

			var computes = this.constructor._computedPropertyNames;

			for (var i = 0, len = computes.length; i < len; i++) {
				var attrName = computes[i];
				mapHelpers.addComputedAttr(this, attrName, this[attrName]);
			}
		}
function () {
			this._computedAttrs = Object.create(null);

			var computes = this.constructor._computedPropertyNames;

			for (var i = 0, len = computes.length; i < len; i++) {
				var attrName = computes[i];
				mapHelpers.addComputedAttr(this, attrName, this[attrName]);
			}
		}
### _setupComputes Sets up computed properties on a Map. Stores information for each computed property on `this._computedAttrs` that looks like:  ``` { // the number of bindings on this property count: 1, // a handler that forwards events on the compute // to the map instance handler: handler, compute: compute  // the compute } ```