详解javascript如何通过async/await优雅地使用filereader-kb88凯时官网登录

filereader的使用机会很多，但是它是异步的，因此很容易出现回调地狱。

我们可以使用async/await特性，它允许我们以同步的方式调用异步代码。

封装成方法

export async function readtextfile(file: file) {
    const reader = new filereader();
    reader.readastext(file);
    return new promise((resolve, reject) => {
        reader.onload = () => resolve(reader.result);
        reader.onerror = () => reject(reader.error);
    });
}
export async function readbinaryfile(file: file) {
    const reader = new filereader();
    reader.readasarraybuffer(file);
    return new promise((resolve, reject) => {
        reader.onload = () => resolve(reader.result);
        reader.onerror = () => reject(reader.error);
    });
}
export async function readastext(file: file) {
    const reader = new filereader();
    reader.readastext(file);
    return new promise((resolve, reject) => {
        reader.onload = () => resolve(reader.result);
        reader.onerror = () => reject(reader.error);
    });
}

使用方法：

(async()=> {
    const buffer1 = await readtextfile(file);
    const buffer2 = await readbinaryfile(file);
    const buffer3 = await readastext(file);
})();

javascript封装成一个class

class filereaderex extends filereader{
    constructor(){
        super();
    }
    #readas(blob, ctx){
        return new promise((res, rej)=>{
            super.addeventlistener("load", ({target}) => res(target.result));
            super.addeventlistener("error", ({target}) => rej(target.error));
            super[ctx](blob);
        });
    }
    readasarraybuffer(blob){
        return this.#readas(blob, "readasarraybuffer");
    }
    readasdata{
        return this.#readas(blob, "readasdataurl");
    }
    readastext(blob){
        return this.#readas(blob, "readastext");
    }
}

使用方法：

(async()=>{
    const buffer1 = await new filereaderex().readasarraybuffer(blob1);
    const buffer2 = await new filereaderex().readasdata;
    const buffer3 = await new filereaderex().readastext(blob3);
})();

typescript封装成一个class

export class filereaderex extends filereader {
    constructor() {
        super();
    }
    private readas(blob: blob, ctx: 'readasarraybuffer' | 'readasdataurl' | 'readastext') {
        return new promise((res, rej) => {
            super.addeventlistener("load", ({target}) => res(target?.result));
            super.addeventlistener("error", ({target}) => rej(target?.error));
            super[ctx](blob);
        });
    }
    readasarraybuffer(blob: blob) {
        return this.readas(blob, "readasarraybuffer");
    }
    readasdata {
        return this.readas(blob, "readasdataurl");
    }
    readastext(blob: blob) {
        return this.readas(blob, "readastext");
    }
}

使用方法：

(async()=>{
    const buffer1 = await new filereaderex().readasarraybuffer(blob1);
    const buffer2 = await new filereaderex().readasdata;
    const buffer3 = await new filereaderex().readastext(blob3);
})();

typescript基于泛型

/**
 * @description 同步调用包装
 * @param promise 需要被调用的异步方法
 */
async function asyncwrap(promise: promise): promise {
    try {
        return await promise;
    } catch (err) {
        return null;
    }
}
export async function filereaderwrap(blob: blob, ctx: 'readasarraybuffer' | 'readasdataurl' | 'readastext'): promise {
    const reader = new filereader();
    reader[ctx](blob);
    return new promise((resolve, reject) => {
        reader.onload = () => resolve(reader.result);
        reader.onerror = () => reject(reader.error);
    });
}

使用方法：

(async()=>{
    const buffer1 = await asyncwrap(filereaderwrap(file, 'readasarraybuffer'));
    const buffer2 = await asyncwrap(filereaderwrap(file, 'readasdataurl'));
    const buffer3 = await asyncwrap(filereaderwrap(file, 'readastext'));
})();