javascript - 如何在出现语法错误的循环中写入 "if"条件并更新列表中的一行

Question

我被困在这之间了。我想循环检查 Prop 索引和 map 索引是否匹配然后更改值

但是，如果我执行以下操作，它会抛出指向 if 的语法错误，请让我知道出了什么问题，这超出了

 import React, {Component} from 'react';

更新.js

class UpdateItem extends Component{

constructor(props){
    super(props);
    this.state={editedVal:''};
    //this.setState({editedVal:this.props.eVal});
    this.handleSubmit=this.handleSubmit.bind(this);
    this.handleChange=this.handleChange.bind(this);
}
handleChange(e)
{this.setState({

    editedVal:e.target.value
    });
 //this.props.eVal=e.target.value;
  }
   handleSubmit(e){
    e.preventDefault();
    alert( this.state.editedVal);
    alert(this.props.eIndx);
   this.props.list.map((item,i)=>{if(this.props.eIndx===i) 
   {alert("s")}else{alert("sd")}});

}
render(){
    return(
       <div>
         <form onSubmit={this.handleSubmit}>
           <input type="text" value={this.state.editedVal?this.state.editedVal:this.props.eVal} onChange={this.handleChange}/>
           <input type="submit" value="update"/>
         </form>
       </div>
    );
}
}

 export default UpdateItem;

添加列表.js

   class AdList extends Component{
   constructor(props){
  super(props);
  this.state={value:'',disArrList:[],editVal:'',editIndx:''}
  this.handleChange=this.handleChange.bind(this);
  this.handleSubmit=this.handleSubmit.bind(this);
  this.delItemRow=this.delItemRow.bind(this);
  this.updateItemRow=this.updateItemRow.bind(this);
  this.editItemValue=this.editItemValue.bind(this);

}

 editItemValue(e)
 {
    alert("edit");
 }

delItemRow(itemName)
{this.setState({disArrList:this.state.disArrList.filter(e1=>e1!==itemName)}) 
;

}

updateItemRow(itemName,itemId)
{
       this.setState({editVal:itemName,editIndx:itemId});
    alert(itemId +"==========="+itemName);
}


handleChange(e){
    this.setState({value:e.target.value});
}

handleSubmit(e){
    e.preventDefault();
    //alert("submit"+this.state.value);
    let mycolletion=this.state.disArrList.concat(this.state.value);
    this.setState({disArrList:mycolletion});
}


render(){
    return(
        <div>
            <div className="Todo">
                <form onSubmit={this.handleSubmit}>
                    <input type="text" value={this.state.value} onChange={this.handleChange}/>
                    <input type="submit" value="Add" />
                </form>
            </div>
            <div>
               <DisplayList  list={this.state.disArrList} removeItem={this.delItemRow} updateItem={this.updateItemRow}/>
            </div>
            <div>
                <UpdateItem list={this.state.disArrList} editItem={this.editItemValue} eVal={this.state.editVal} eIndx={this.state.editIndx}/>
            </div>

        </div>
        );
}
 } 

export default AdList;

Answer 1

if 是语句，不是表达式。您必须使用大括号箭头函数才能使用 if。

this.props.list.map((item, i) => {
  if (this.props.eIndx === i) {
    alert("s");
  } else {
    alert("sd");
  }
  // map should always return something,
  // or you'll end up with a list of `undefined`s.
  //Otherwise use `forEach`.
  return 'something';
});