react upload preview

gistfile1.txt

handleChange(e){
        console.log('file',e.target.files)
        let files = [...e.target.files]
        let that = this
        let fileList = []
        files.map((v,n)=>{
            let reader = new FileReader(e);
            reader.onload = function () {
                let url = event.target.result
                fileList.push({
                    originFile:v,
                    url:url||''
                })

                if(fileList.length===files.length){
                    that.setState({
                        fileList
                    })
                }

            }
            reader.readAsDataURL(v);
        })
    }