Underscore _.each callback when finished?

问题:

Is there a callback for when underscore is finished it's _.each loop because if I console log immediately afterwards obviously the array I am populating with the each loop is not available. This is from a nested _.each loop.

_.each(data.recipe, function(recipeItem) {
    var recipeMap = that.get('recipeMap');
    recipeMap[recipeItem.id] = { id: recipeItem.id, quantity: recipeItem.quantity };
});
console.log(that.get('recipeMap')); //not ready yet.

回答1:

The each function in UnderscoreJS is synchronous which wouldn't require a callback when it is finished. One it's done executing the commands immediately following the loop will execute.

If you are performing async operations in your loop, I would recommend using a library that supports async operations within the each function. One possibility is by using AsyncJS.

Here is your loop translated to AsyncJS:

async.each(data.recipe, function(recipeItem, callback) {
    var recipeMap = that.get('recipeMap');
    recipeMap[recipeItem.id] = { id: recipeItem.id, quantity: recipeItem.quantity };
    callback(); // show that no errors happened
}, function(err) {
    if(err) {
        console.log("There was an error" + err);
    } else {
        console.log("Loop is done");
    }
});

回答2:

Another option is to build your callback function into the each loop on the last execution:

_.each(collection, function(model) {
    if(model.collection.indexOf(model) + 1 == collection.length) {
         // Callback goes here
    }
});

Edit to add:

I don't know what your input/output data looks like but you might consider using _.map instead, if you're just transforming / rearranging the contents