Accessing `this` in class function is undefined

Question

I am trying to implement a throttle method inside a class that takes as the second argument some class properties but I can't access the class properties because this is undefined.

I have reproduced the code in a simpler manner to demonstrate the issue:

function someThrottleFunction(a, b) {
  // doesn't really matter what is in here
}

class cname {
  constructor(prop1) {
    this.prop1 = prop1;
  }
  func = someThrottleFunction(() => {}, this.prop1.time);
}

let a = new cname({ time: 3000 });

you can see a live code error demo here: https://codesandbox.io/s/x7yqy933qq

Any suggestions on how to rewrite this in a working manner are greately appreciated.

@paulsm4 I don't know if this is scientifically backed, but anecdotally it's easier on the eyes for some (most?) people. — Jared Smith
– Jared Smith, Commented Dec 27, 2018 at 0:32
@paulsm4 Maybe it's also because of the AMOLED screens which doesn't drain power when displaying black content — Alex C
– Alex C, Commented Dec 27, 2018 at 0:36

CertainPerformance · Accepted Answer · 2018-12-27 01:02:33Z

3

The problem is that the func is assigned to before the constructor runs:

function someThrottleFunction(a, b) {
  // doesn't really matter what is in here
}

class cname {
  constructor(prop1) {
    console.log('constructor running');
    this.prop1 = prop1;
  }
  func = (console.log('func being assigned to'), someThrottleFunction(() => {}, this.prop1.time));
}

let a = new cname({ time: 3000 });

You might assign at the end of the constructor instead:

function someThrottleFunction(a, b) {
  // doesn't really matter what is in here
}

class cname {
  constructor(prop1) {
    this.prop1 = prop1;
    this.func = someThrottleFunction(() => {}, this.prop1.time);
  }
}

let a = new cname({ time: 3000 });

edited Dec 27, 2018 at 1:02

answered Dec 27, 2018 at 0:25

CertainPerformance

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Comments

ic3b3rg · Accepted Answer · 2018-12-27 00:30:10Z

1

It looks like you intended for func to be a function:

function someThrottleFunction(a, b) {
  console.log(b)
}

class cname {
  constructor(prop1) {
    this.prop1 = prop1;
  }
  func() { 
    someThrottleFunction(() => {}, this.prop1.time);
  }
}

let a = new cname({ time: 3000 });
a.func()

or

function someThrottleFunction(a, b) {
  console.log(b)
}

class cname {
  constructor(prop1) {
    this.prop1 = prop1;
  }
  func = () => { 
    someThrottleFunction(() => {}, this.prop1.time);
  }
}

let a = new cname({ time: 3000 });
a.func()

answered Dec 27, 2018 at 0:30

ic3b3rg

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