Alastair Alastair -4 years ago 137
Javascript Question

Bluebird promises - how to explode an array, then map it?

If I have an array:

['one.html','two.html','three.html']


how could I explode that array, apply a chain of promises to it, then combine it back together again? At the moment my code is like this:

Promise.map(['one','two','three'], function(i) {
dbQuery('SELECT ' + i);
}).then(function(results) {
// This has an array of DB query results
});


I'm imagining something like:

Promise.map(['one','two','three'], function(i) {
dbQuery('SELECT ' + i);
})
.explode()
.then(function(result) {
// Individual result
})
.combine()
.then(function(results) {
// Now they're back as an array
});


Now, I know Bluebird doesn't have these functions, so I'm wondering what the correct Promise-y way is of doing this?

Answer Source

You can use a chain of maps:

Promise.map(['one','two','three'], function(i) {
    return dbQuery('SELECT ' + i);
}).map(function(result) {
    // Individual result
}).map(function(result) {
    // Individual result
}).map(function(result) {
    // Individual result
}).then(function(results) {
    // Now they're back as an array
});

However the above will not be as concurrent as

Promise.map(['one','two','three'], function(i) {
    return dbQuery('SELECT ' + i).then(function(result) {
        // Individual result
    }).then(function(result) {
        // Individual result
    }).then(function(result) {
        // Individual result
    })
}).then(function(results) {
    // Now they're back as an array
});
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