The `flatten` function takes an array of arrays and flattens them to a single array, removing one level of nesting. It does not recursively flatten multiple levels of nesting.

Try push: https://treeherder.mozilla.org/#/jobs?repo=try&revision=fe212b807e13

Comment on attachment 8736069 [details] [diff] [review] Add the ThreadSafeDevToolsUtils.flatten utility Jordan is on PTO, so Jim gets another review!

Comment on attachment 8736069 [details] [diff] [review] Add the ThreadSafeDevToolsUtils.flatten utility Review of attachment 8736069 [details] [diff] [review]: ----------------------------------------------------------------- If the identities I suggest here are actually right, then perhaps it's best to just use the primitive that JS readers would be familiar with directly, instead of introducing new names for them. ::: devtools/shared/ThreadSafeDevToolsUtils.js @@ +248,5 @@ > + const length = inList.length; > + for (let i = 0; i < length; i++) { > + outList.push(inList[i]); > + } > + return outList; If this is required to mutate outList, then I think this is equivalent to outList.push.apply(inList). If only its return value matters and its arguments are consumed, then this is equivalent to outList.concat(inList). But I am not at all comfortable with the JS array operations, so check my claims. @@ +259,5 @@ > + * @param {Array<Array<Any>>} lists > + * @return {Array<Any>} > + */ > +exports.flatten = function(lists) { > + return lists.reduce(flattenReducer, []); I think this is just [].concat.apply(lists).

The `flatten` function takes an array of arrays and flattens them to a single array, removing one level of nesting. It does not recursively flatten multiple levels of nesting.

We should probably just use lodash (or the subset that isn't covered by the ES spec) at some point

We should probably just use left-pad...

</snark> We should probably replace this with Array.prototype.flatten once SM implements it.