index.js

{
    const userId = 'fb272868-027b-4c7e-b813-b8769c608724'; // can be taken out from almost any requests in xero
    const startDate = new Date("2019-04-06"); // start of period where time entries should be generated, format: yyyy-mm-dd
    const endDate = new Date("2019-04-07"); // end of period where time entries should be generated, format: yyyy-mm-dd

    const yourTimeEntries = [{
        name: 'Other',
        hours: 0.5,
        description: 'Scrum Daily Meeting'
    }, {
        name: 'Consulting',
        hours: 3.5,
        description: 'Team support (consultations, tech design, issues investigation, priorities confirmation and etc)'
    }, {
        name: 'Bug Development',
        hours: 2,
    }, {
        name: 'Feature Development',
        hours: 2,
    }];


    var url = 'https://go.xero.com/api/projects/projects/db637125-7cd6-4022-a56f-d991712f4cad/time';
    const getTasksUrl = 'https://go.xero.com/api/projects/projects/db637125-7cd6-4022-a56f-d991712f4cad/tasks';

    function getAuthorization() {
        var tokenObj = JSON.parse(sessionStorage.getItem('oidc.user:https://identity.xero.com:xero_business_go'));
        return {'authorization' : `Bearer ${tokenObj.access_token}`};
    }

    // Get list of available task (other, feature development, consulting and so on)
    function getTasks() {
        return fetch(getTasksUrl, {headers: getAuthorization()});
    }

    // pack data in way as xero api expects
    function getData(stringDateUtc, tasks, yourTimeEntries) {
        const data = [];
        yourTimeEntries.forEach(timeEntry => {
            const task = tasks.find(task => task.name === timeEntry.name);
            if (!task){
                throw Error("Task is not found")
            }
            data.push({
                taskId: task.taskId,
                userId: userId,
                duration: timeEntry.hours * 60,
                description: timeEntry.description,
                dateUtc: stringDateUtc
            })
        });
        return data;
    }

    function postDateTimeEntry(dayTimeEntry) {
        return fetch(url, {
            method: 'POST',
            body: JSON.stringify(dayTimeEntry),
            headers:{
                'Content-Type': 'application/json',
                ...getAuthorization()
            }
        })
    }

    async function postTimeEntries() {
        let tasks;
        try {
            const tasksPromise = await getTasks();
            const tasksResponse = await tasksPromise.json();
            tasks = tasksResponse.items;
        } catch(e) {
            new Error(`Cannot get tasks\n ${e}`);
        }

        let timeEntryPromises = []; // {promise, data}

        for (let date = startDate; date <= endDate; date.setDate(date.getDate() + 1)) {
            const dayTimeEntries = getData(date.toISOString(), tasks, yourTimeEntries);
            dayTimeEntries.forEach(dayTimeEntry => {
                timeEntryPromises.push({promise: postDateTimeEntry(dayTimeEntry), data: dayTimeEntry});
            });
        }
        // logic to retry failed requests
        while (timeEntryPromises.length > 0) {
            const results = await Promise.all(timeEntryPromises.map(p => p.promise.catch(e => e)));
        
            const failedPromises = results.filter(result => result.status != 201);

            let tryAgainTimeEntryPromises = []
            // find promises-data objects, which requests have been failed   
            failedPromises.forEach(invalidResult => {
                const posInvalidResult = results.indexOf(invalidResult);
                tryAgainTimeEntryPromises.push(timeEntryPromises[posInvalidResult]);
            });
            
            timeEntryPromises = tryAgainTimeEntryPromises;

            timeEntryPromises.forEach(timeEntryPromise => {
                const newAttemptPromise = postDateTimeEntry(timeEntryPromise.data);
                timeEntryPromise.promise = newAttemptPromise;
                console.log(`Trying to add time entry again for ${JSON.stringify(timeEntryPromise.data)}`);
            });
        }
        alert('All your time tracking records have been added');
    }

    postTimeEntries();
}