使用承诺进行分页的最佳方式是什么?

What is the best way to approach pagination with Promises?

本文关键字：最佳 方式 是什么 分页 承诺      更新时间：2023-09-26
我

和我的朋友正在处理承诺，我们确保在返回最初的调用之前获得所有页面的数据。有没有更微不足道的方法可以解决这个问题？

function getDocuments(startIndex, result, entries) {
    startIndex = typeof startIndex !== 'undefined' ? startIndex : 0;
    result = typeof result !== 'undefined' ? result : {};
    entries = typeof entries !== 'undefined' ? entries : [];
    // build our entries set with the result parameter
    for(var i in result.items) {
        try
        {
            var id = result.items[i].id;
            var name = result.items[i].name;
            var content = result.items[i].content;
            var entry = { "id": id, "name": name, "content": content };
            entries.push(entry);
        }
        catch(e) {
        }
    }
    // return a promise that fulfills a promise that then returns either a promise or a result.
    return new Promise(function(fulfill, reject) {
        // fulfill the promise and resolve the value, we pass a recursive promise as the value.
        fulfill(documentClient.getDocuments({ "startIndex": startIndex }).then(function(result) { // once our request is made, let's check the page count.
            var startIndex = result.startIndex;
            var pageSize   = result.pageSize;
            var totalCount = result.totalCount;
            if (startIndex + pageSize <= totalCount) { // if our current position is not at the end of the pages, return a promise with our current data and our current entries.
                return getDocuments(startIndex + pageSize, result, entries);
            }
            return entries; // otherwise our entries will bubble back up the stack and be resolved into the initial fulfill value.
        }));
    });
}
getDocuments().then(function(d) { console.log(d.length); });

我的调整：

function getDocuments(startIndex, result, entries) {
    startIndex = typeof startIndex !== 'undefined' ? startIndex : 0;
    result = typeof result !== 'undefined' ? result : {};
    entries = typeof entries !== 'undefined' ? entries : [];
    // build our entries set with the result parameter
    // ...
    // return a promise that fulfills a promise that then returns either a promise or a result.
    return documentClient.getDocuments({ "startIndex": startIndex }).then(function(result) { // once our request is made, let's check the page count.
        var startIndex = result.startIndex;
        var pageSize   = result.pageSize;
        var totalCount = result.totalCount;
        if (startIndex + pageSize <= totalCount) { // if our current position is not at the end of the pages, return a promise with our current data and our current entries.
            return getDocuments(startIndex + pageSize, result, entries);
        }
        return entries; // otherwise our entries will bubble back up the stack and be resolved into the initial fulfill value.
    });
}
getDocuments().then(function(d) { console.log(d.length); });

是的，你可以像这样链接承诺，因为documentClient.getDocuments返回一个承诺。

function getDocuments(startIndex, result, entries) {
    // ...
    return documentClient.getDocuments({ "startIndex": startIndex }).then(function(result) {
        // ...
        return entries; // otherwise our entries will bubble back up the stack and be resolved into the initial fulfill value.
    });
}
getDocuments().then(function(d) { console.log(d.length); });

在getDocuments中有一个代码路径，该路径不以新承诺结尾

这是一个简单的例子

function defer(fn) {
    setTimeout(fn, 100);
}
function promiseChain(i, msg) {
    if (i <= 0) return msg; // end code path
    return new Promise((res, rej) => {
        defer(e => res(promiseChain(i - 1, msg)));
    });
}
promiseChain(10, "Hello World!").then(data => console.log(data));
// "Hello World!" logged after ten 100ms timeouts
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