在觀察template執(zhí)行的時(shí)候，如下圖所示：展開ng-template時(shí)：

會(huì)觸發(fā)函數(shù)??property的執(zhí)行：

/*** @license* Copyright Google LLC All Rights Reserved.** Use of this source code is governed by an MIT-style license that can be* found in the LICENSE file at https://angular.io/license*/ /*** Update a property on a selected element.** Operates on the element selected by index via the {@link select} instruction.** If the property name also exists as an input property on one of the element's directives,* the component property will be set instead of the element property. This check must* be conducted at runtime so child components that add new `@Inputs` don't have to be re-compiled** @param propName Name of property. Because it is going to DOM, this is not subject to* renaming as part of minification.* @param value New value to write.* @param sanitizer An optional function used to sanitize the value.* @returns This function returns itself so that it may be chained* (e.g. `property('name', ctx.name)('title', ctx.title)`)** @codeGenApi*/ function ??property(propName, value, sanitizer) {const lView = getLView();const bindingIndex = nextBindingIndex();if (bindingUpdated(lView, bindingIndex, value)) {const tView = getTView();const tNode = getSelectedTNode();elementPropertyInternal(tView, tNode, lView, propName, value, lView[RENDERER], sanitizer, false);ngDevMode && storePropertyBindingMetadata(tView.data, tNode, propName, bindingIndex);}return ??property; }

如果想查看第二行l(wèi)ayoutName$變量的值，在debugger里查看arguments:

展開source:

source._value里的header就是layoutName$準(zhǔn)備emit出去的值。

更多Jerry的原創(chuàng)文章，盡在：“汪子熙”:

總結(jié)

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