Angular: Performance implication of using object literals in component template for ng-template context with ngTemplateOutlet

user_2724917 0
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What are the performance implications of using an object literal in the template when passing context to ng-template?

<ng-container *ngTemplateOutlet="template;context:{ field: value };"></ng-container>

as opposed to:

<ng-container *ngTemplateOutlet="template;context:context;"></ng-container>

context = { field: value }

Is change detection going to run more often in the first case, since it's (presumably) creating a new object?

https://github.com/angular/angular/blob/c2868de25a0fe4e14e4da4aae6aa2d5867711d05/packages/common/src/directives/ng_template_outlet.ts

  /**
   * We need to re-create existing embedded view if:
   * - templateRef has changed
   * - context has changes
   *
   * We mark context object as changed when the corresponding object
   * shape changes (new properties are added or existing properties are removed).
   * In other words we consider context with the same properties as "the same" even
   * if object reference changes (see https://github.com/angular/angular/issues/13407).
   */
  private _shouldRecreateView(changes: SimpleChanges): boolean {
    const ctxChange = changes['ngTemplateOutletContext'];
    return !!changes['ngTemplateOutlet'] || (ctxChange && this._hasContextShapeChanged(ctxChange));
  }

Judging by this I would say it does make a difference because the function call is more expensive if "ngTemplateOutletContext" is in changes. And it always would be there if it's defined as an object literal in the template. This assumes that a new object is created every cycle. Is this assumption wrong?

angular-template angular
1 Answers

I stumbled against this article explaining that a literal object in templates doesn't imply a new instance on every detect cycle. I checked it out with a modern versions of Angular and its behavior is the same. So, I suppose that construction like in your code snippet is okay and it can be used without any problem.

user_109719100
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