js从文件流获取minetype

js从文件流获取minetype

 {
          // @ts-ignore
          const file = ev.target.files[0];
          // ext get file type 
          console.log(file, file.type);
          const fr = new FileReader();
          fr.addEventListener('load', function () {
            // @ts-ignore
            // eslint-disable-next-line react/no-this-in-sfc
            let u = new Uint8Array(this.result);
            const a = new Array(u.length);
            let i = u.length;
            while (i--)
              // map to hex
              a[i] = (u[i] < 16 ? '0' : '') + u[i].toString(16);
            // @ts-ignore
            u = null; // free memory
            // hex value
            console.log(a); 
          });
          fr.readAsArrayBuffer(file);
        }}
      />
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• 常见文件类型 hex前缀对应可以在这里查询 https://mimesniff.spec.whatwg.org/#byte-pattern