en.javascript.info/1-js/04-object-basics/04-object-methods/8-chain-calls/task.md

importance: 2

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Chaining

There's a ladder object that allows to go up and down:

let ladder = {
  step: 0,
  up() { 
    this.step++;
  },
  down() { 
    this.step--;
  },
  showStep: function() { // shows the current step
    alert( this.step );
  }
};

Now, if we need to make several calls in sequence, can do it like this:

ladder.up();
ladder.up();
ladder.down();
ladder.showStep(); // 1

Modify the code of up, down and showStep to make the calls chainable, like this:

ladder.up().up().down().showStep(); // 1

Such approach is widely used across JavaScript libraries.