Skip to main content

underscore.js extend


underscore.js is a javascript utility library.

Let us understand the extend method of this very useful library.
_.extend is for extending a given object with all the properties of the passed-in object(s)

Here is an example, we have three objects aObj, bObj, cObj and we want to combine them into single object.


















Using _.extend is a simple way of combining these objects. And before trying out the example don't forget to import the underscore.js library

Now access the source code of underscore.js and look for the extend method. This is how it looks like

This uses functional programming style. 
createAssigner takes two inputs and returns a function. The two inputs are
(1) keysFunc 
(2) defaults

Since it is returning a function, so a closure is formed, and the returned function remembers the two inputs
Looking at the source code from the line (keys = keysFunc(source)) it is evident that keysFunc is a function itself.
And from the line _.extend = createAssigner(_.allKeys) we can understand that allKeys is the function that is passed as input for keysFunc. Here is the allKeys function from underscore.js



To the function that is returned by createAssigner, we pass the objects whose properties have to be combined as the inputs. In our example aObj, bObj and cObj are passed to the return function of createAssigner function.

aObj is the source object, bObj and cObj are the objects that have to be merged with aObj.
Note that extend mutates the aObj. The resultant aObj has the properties from all the objects passed for merging with aObj







Labels:

Comments

Post a Comment

Popular posts from this blog

Kubernetes: 15. Multiple Schedulers

Custom Scheduler Kubernetes allows to create custom schedulers There can be multiple schedulers running at a same time apart from the default scheduler or A custom scheduler can replace the default kube-scheduler to become the default one So a few pods that requires additional checks apart from taints and toleration, node affinity can go through the custom scheduler before getting scheduled on the node Whereas the rest of the pods can go through the default kube-scheduler Create Custom Scheduler We can either download the kube-scheduler and run it as a service or alternatively create it using a static pod Below here we are downloading the binaries to run it The property scheduler-name is used to define the name of the scheduler, if not set then it will be defaulted to default-scheduler For your custom schedulers, update this property name to set a custom name for your scheduler For Static pods, the name can be updated directly in the pod-definition file Use kubectl create -f <pod-de...
Post a Comment
Read more

Kubernetes: 19. Configure Application

Configuring application consists of Configuring commands and arguments on applications Configuring environment variables Configuring secrets Docker Commands docker run ubuntu  -> Runs ubuntu container and exit, container CMD is set to [bash], so the container quitely exits docker run ubuntu echo "Hello World" -> Runs ubuntu container, prints "Hello World" exits quitely. To update the default settings, create your own image from the base image lets call this ubuntu-sleeper image FROM ubuntu CMD sleep 5 CMD can also be mentioned in the JSON format like CMD ["sleep", "5"] Note that with JSON format the first element should always be the command to execute,  for eg, it CANNOT be ["sleep 5"] Run build the new ubuntu-sleeper image and run the new image docker build -t ubuntu-sleeper .  -> Build the image docker run ubuntu-sleeper -> Run the new image So the new image will launch ubuntu container, sleep for 5 seconds and quitely ex...
Post a Comment
Read more

Kubernetes: 8. Labels & Selectors

Labels Labels are a way of grouping the objects While Kubernetes understands the objects it create, it is easier to identify the objects by using custom labels With labels you group the objects by types (Pods, Services, ReplicaSet etc) or by Applications For a pod, labels are defined under the metadata section Selectors Selectors are used to filter the objects using labels defined on them Using kubectl and selector pods can be listed by filtering on the labels attached to them If a Selector has multiple labels, they are understood as logical AND, which means pods must match all labels. pod-definition.yaml apiVersion: v1 kind: Pod metadata:      name: myapp-pod      labels:           app: myapp           location: IN spec:      containers:      - name: nginx-container        image: nginx kubectl get pods ...
Post a Comment
Read more