import {Component} from '@angular/core';

@Component({
  selector: 'hello-world',
  templateUrl: 'hello-world.html'
})

class HelloWorld {
  constructor() {
    console.log('constructor被调用，但和Angular无关');
  }
}

// 生成类实例，此时会调用constructor
new HelloWorld();

import {Component, OnInit} from '@angular/core';

@Component({
  selector: 'hello-world',
  templateUrl: 'hello-world.html'
})

class HelloWorld implements OnInit {
  constructor() {

  }

  ngOnInit() {
    console.log('ngOnInit被Angular调用');
  }
}

import { Component, ElementRef } from '@angular/core';

@Component({
  selector: 'hello-world',
  templateUrl: 'hello-world.html'
})
class HelloWorld {
  constructor(private elementRef: ElementRef) {
    // 在类中就可以使用this.elementRef了
  }
}

// hello-world.ts
import { Component, Input, OnInit } from '@angular/core';

@Component({
  selector: 'hello-world',
  template: `<p>Hello {{name}}!</p>`
})
class HelloWorld implements OnInit {
  @Input()
  name: string;

  constructor() {
    // constructor中还不能获取到组件/指令中被传入的数据
    console.log(this.name);   // undefined
  }

  ngOnInit() {
    // ngOnInit中已经能够获取到组件/指令中被传入的数据
    console.log(this.name);   // 传入的数据
  }
}