如何绑定`this`来减少？

Question

我有一个简单的减速器,如何this从外部绑定以在减速器内部使用this.teacherInstance？

this.teachersDropMenu = this.plans.reduce(function (teacherIdArr, teacher) {
  if (teacherIdArr.indexOf(teacher.teacherId) == -1) {
     teacherIdArr.push(this.teacherInstance.getTeacherModelById(teacher.teacherId));
  }
  return teacherIdArr;
}, []);

Answer 1

使用明确的结合有 Function.prototype.bind:

this.teachersDropMenu = this.plans.reduce(function (teacherIdArr, teacher) {
   if (teacherIdArr.indexOf(teacher.teacherId) == -1) {
      teacherIdArr.push(this.teacherInstance.getTeacherModelById(teacher.teacherId));
   }
   return teacherIdArr;
}.bind(this), []);

使用闭包/引用:

const self = this;
this.teachersDropMenu = this.plans.reduce(function (teacherIdArr, teacher) {
   if (teacherIdArr.indexOf(teacher.teacherId) == -1) {
      teacherIdArr.push(self.teacherInstance.getTeacherModelById(teacher.teacherId));
   }
   return teacherIdArr;
}, []);

使用没有自己的ES6箭头函数this,保留"外部":

this.teachersDropMenu = this.plans.reduce((teacherIdArr, teacher) => {
   if (teacherIdArr.indexOf(teacher.teacherId) == -1) {
      teacherIdArr.push(this.teacherInstance.getTeacherModelById(teacher.teacherId));
   }
   return teacherIdArr;
}, []);