Array.prototype.slice.call()方法详解

• slice:用来截取截取字符串方法
• Array: javascript的一个引用类型，其原型prototype上有一个方法叫slice
• call和apply ： 用来改变对象中函数内部的this引用，使得函数可以随便换‘妈妈’

为什么不直接用 arguments.slice(1)呢 不是一样的么?

答案是不一样。

Array.prototype.slice.call(arguments, 1)可以理解成是让arguments转换成一个数组对象，让arguments具有slice()方法。要是直接写arguments.slice(1)会报错。

arguments 是object 不是Array ，他的原型上没有slice方法

原理：

Array.prototype.slice.call(arguments)能将具有length属性的对象转成数组

var a={length:2,0:'first',1:'second'};//类数组,有length属性，长度为2，第0个是first，第1个是second
console.log(Array.prototype.slice.call(a,0));// ["first", "second"],调用数组的slice(0);

var a={length:2,0:'first',1:'second'};
console.log(Array.prototype.slice.call(a,1));//["second"]，调用数组的slice(1);

var a={0:'first',1:'second'};//去掉length属性，返回一个空数组
console.log(Array.prototype.slice.call(a,0));//[]

function test(){
  console.log(Array.prototype.slice.call(arguments,0));//["a", "b", "c"]，slice(0)
  console.log(Array.prototype.slice.call(arguments,1));//["b", "c"],slice(1)
}
test("a","b","c");

将函数的实际参数转换成数组的方法：

1、

var args = Array.prototype.slice.call(arguments);

2、

var args = []; 
for (var i = 1; i < arguments.length; i++) { 
    args.push(arguments[i]);
}

 3、

var toArray = function(s){
    try{
        return Array.prototype.slice.call(s);
    } catch(e){
        var arr = [];
        for(var i = 0,len = s.length; i < len; i++){
            //arr.push(s[i]);
               arr[i] = s[i];  //据说这样比push快
        }
         return arr;
    }
}

将函数的实际参数转换成数组的方法的实际应用：

表单申请时，upload组件上传多张图片时候，能够左右切换预览所有上传的图片；

表单申请后，打开upload组件也能够预览多张图片

代码如下

import Viewer from "viewerjs";
预览组件的版本号："viewerjs": "^1.10.5",

 /**关闭图片 */
  handleCancel = () => this.setState({ previewVisible: false });
  /**处理图片 */
  handlePreview = async (file: UploadFile, className: string) => {
    if (!file.url && !file.preview) {
      file.preview = await getBase64(file.originFileObj as Blob) as string;
    }
    if ([".pdf", ".docx", ".doc"].some(i => file.response?.data.replace(/\s/g, "")?.includes(i)) || [".pdf", ".docx", ".doc"].some(i => file.url?.replace(/\s/g, "")?.includes(i))) {
      this.setState({
        previewImage: file?.url || file?.preview as string,
        previewVisible: true,
        fileUrl: file.response?.data.replace(/\s/g, ""),
      });
    } else {
      const dom = document.querySelector(`.${className} .ant-upload-list`);
      const url = file.url || file.thumbUrl || file.preview;
      const domSrcList = Array.prototype.slice.call(document.querySelectorAll(`.${className} .ant-upload-list img`)).map(i => i.src);
      if (dom) {
        const gallery = new Viewer(dom as HTMLElement, {
          initialViewIndex: domSrcList.indexOf(url) !== -1 ? domSrcList.indexOf(url) : 0,
          hidden: () => {
            gallery.destroy();
          },
        });
        gallery.show();
      }
    }
  }


 /** 处理上传 */
  handleChange = async (data: UploadChangeParam<UploadFile<any>>) => {
    const fun = () => {
      if (data.file.response) {
        if (data.file.response.data) {
          for (let i of data.fileList) {
            if (i.thumbUrl?.includes("base64")) {
              i.thumbUrl = i.response?.data || i.thumbUrl;
            }
          }
        }
      }
    }
    fun();
  }



render() {

<div className="clearfix sycnssmj">
            <Form.Item>
              {getFieldDecorator("sycnssmj", {
                valuePropName: "sycnssmj",
                getValueFromEvent: (e: UploadChangeParam) => {
                  return e.fileList;
                },
                rules: [
                  {
                    required: checkType ? true : false,
                    message: "文件必须上传！",
                  },
                  { validator: checkedUploadSuccess },
                ],
                initialValue: defaultValue && [...fileListFun(defaultValue.sycnssmj as File[])],
              })(<Upload
                accept="image/*,.pdf,.docx"
                key={JSON.stringify(defaultValue && [...fileListFun(defaultValue.sycnssmj as File[])])}
                defaultFileList={defaultValue && [...fileListFun(defaultValue.sycnssmj as File[])]}
                name="file"
                multiple
                transformFile={transformFile}
                listType="picture"
                action={`${window.config.backEnd}/api/v1/business/file/upload`}
                method="POST"
                headers={{
                  Authorization: users && `Bearer ${users.access_token}`,
                }}
                disabled={globelDisable}
                onPreview={(file) => this.handlePreview(file, "sycnssmj")}
                onChange={this.handleChange}
              >
                {globelDisable ? null : <FileButton>{uploadButton}</FileButton>}
              </Upload>)}
            </Form.Item>
          </div>

}

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