Passing code into the function that depends on it.
Hard to describe. Easy to understand through example.
Benefits:
- separation of concerns
- thereby all the benefits of that, modularity, etc
Example
Dependent Code
//not using dependency injection
class Entry{
private data: any;
private saveSpot: "local" | "cloud"
//these arguments are optional sometimes, required others
//logic for how to interact with the save location is buried
//inside the Entry object
save(directory?: string, cloudCredentials?: string){
if(this.saveSpot === "local"){
//code to save locally
//depends on directory arg
return
}
if(this.saveSpot === "cloud"){
//code to save to cloud
//depends on cloud arg
return
}
}
} With Dependency Injection
interface iSaveSpot{
save(): function
}
class localSave implements iSaveSpot{
private directory: string
constructor(loc: string){
this.directory = loc;
}
save(){
//code to save locally here
}
}
class cloudSave implements iSaveSpot{
private credentials: object
constructor(creds: object){
this.credentials = creds;
}
save(){
//code to save to cloud here
}
}
class Entry{
private data: any;
private saveSpot: saveSpotInterface
save(){
//zero dependent code, Entry doesn't have to know
//where it's saving or what specific things have
//to happen to perform the save function
this.saveSpot.save();
}
}