React

Question 1

React component must act like pure function with respect to their props

Answer 1

React component must act like pure function with respect to their props

Question 2

Js react callback binding

Answer 2

If you refer to a method without () after it, you should bind that method. 
In constructor: this.handleClick = this.handleClick.bind(this);
Or: use class field syntax. Check React Doc main concepts, 6
onClick ={{ () => this.handleClick()}}

Question 3

空格还是逗号

Answer 3

tag里面，各等式之间空格，object里，各：pair之间用逗号

Question 4

&&

Answer 4

true ‘&&’ expression evaluates to expression

false && expression evaluates to false

Question 5

? :

Answer 5

condition? true: false

Question 6

Key

Answer 6

Kay is a special string attribute you need to include when creating lists of elements

<li>{...}</li>

Most often, you should use id for key
Not recommended to use index

Question 7

Key more

Answer 7

Key应该用在构建一组list中，而不是单个li组件。通常在map（）call中

Question 8

Object.keys()

Answer 8

???

return array with keys

Question 9

Form, controlled components

Answer 9

用setState来控制form的value，开始，this.state规定了value，如果没有包在onChange中的setState来改变value的话，用户是无法输入或更改信息的。而onChange保证了信息的实时更新，不仅仅是UI中的变化，也包括实时的this.state.value
handleChange(event) {
this.setState({value: event.target.value});
}

onChange={this.handleChange}

Question 10

controlled components, onSubmit preventDefault()

Answer 10

html 自带的，submit以后要refresh浏览器，更新state并把数据传送到后端，React controlled components 自动完成这些，不再需要refresh，而且会造成错误，所以在submit的function里要加入event.preventDefault()

Question 11

parseInt; parseFloat（string)

Answer 11

User输入的都是string，用这些转换

Question 12

Object后面用. 还是[]

Answer 12

[‘key’]

.key

Question 13

props and state

Answer 13

props read only;

state could be modified

Question 14

Controlled components for multiple inputs

Answer 14

Check class material or react doc

Question 15

map()经验

Answer 15

map =>后面如果是跟html element，一定不能加｛｝

Question 16

class 里面新的method里的变量 经验教训

Answer 16

前面一定要加var或者const