Working with the constructor parameters in TypeScript

Question

As shown in the image below, I need to manipulate the input parameter of the constructor that is commandsList but it gave an unknown variable, even with using the this. with it.

I wounder that it accepted this parameter and passed it as an input paramter for another method in the same class, that forced me to write a separate method to handle the few lines I need.

Any help?

Saravana · Accepted Answer · 2017-01-19 09:57:02Z

5

You have to make it an instance variable. Currently it is only a parameter. You can create auto instance variables from constructors like this

constructor(private commandslist: ICommandList) {
   console.log(this.commandslist);
}

Or if you prefer to have it declared explicitly:

private commandslist: ICommandList;

constructor(commandslist: ICommandList) {
    this.commandslist = commandslist;
    console.log(this.commandslist);
}

edited Jan 19, 2017 at 9:57

answered Jan 19, 2017 at 9:42

Saravana

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2 Comments

theUtherSide Over a year ago

Although I usually prefer more-explicit. I like the first approach in this case. It's soo clean, and TS takes care of the rest.

Lee Richardson Over a year ago

FYI I think they're officially called "parameter properties", not "auto instance variables". typescriptlang.org/docs/handbook/classes.html

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