Calling a function from inside the Javascript constructor

Question

Is it possible to call a function from inside the Javascript constructor like this:

class Blockchain {

   constructor(genesisBlock) {

     this.blocks = []
     addBlock(genesisBlock)
   }

   addBlock(block) {

      if(this.blocks.length == 0) {
        block.previousHash = "0000000000000000"
      }
   }

}

I get the following:

addBlock is not defined

Thanks KevBot. If you can post this as answer I can accept it :) — john doe
– john doe, Commented Jan 16, 2018 at 16:31

KevBot · Accepted Answer · 2018-01-16 16:33:12Z

1

Yes, the method is a prototypical method, and needs to be called from the instance of the class (by using this):

...
constructor(genesisBlock) {
    this.blocks = []
    this.addBlock(genesisBlock)
}
...

answered Jan 16, 2018 at 16:33

KevBot

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Comments

AL-zami · Accepted Answer · 2018-01-16 17:21:47Z

0

Why you are getting this error?

When you are calling addBlock function inside the constructor in a following manner

   constructor(genesisBlock) {

     this.blocks = []
     addBlock(genesisBlock)
   }

It is looking for a global function called addBlock.But it can't find any.That's why it throws you an error.Your addBlock is a method of Blockchain class.Instances of Blockchain class will inherit it when instantiated.So you need to invoke it with 'this.addBlock'

 constructor(genesisBlock) {

     this.blocks = []
     this.addBlock(genesisBlock)
   }

edited Jan 16, 2018 at 17:21

answered Jan 16, 2018 at 16:38

AL-zami

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