/invariant-talk

Lunch and Learn Slides for Invariant

Invariant

What is an Invariant?

An expression whose value doesn't change during program execution

How can we use this?

Assert state which your program assumes to be true.

Usage

npm install invariant

var invariant = require('invariant');

// No errors
invariant(true, 'This will not throw');

// Error: Invariant Violation: This will throw an error with this message
invariant(false, 'This will throw an error with this message');

Real World


export dummyMiddleware = ({ dispatch }) => next => action => {
    ...

    invariant(
      actionTypes.length === 3,
      'You must provide 3 action types, one for PENDING, FULFILLED, and REJECTED'
    );

    invariant(
      actionTypes.every(i => typeof i === 'string'),
      'Every action type must be a string'
    );

    const { actionTypes } = action;
    const [ PENDING, FULFILLED, REJECTED ] = actionTypes;

    ...
}

Thank You