In the JavaScript.info tutorial, the following example is incorrect:

ladder.up().up().down().showStep().down().showStep(); // shows 1 then 0

It actually throws this error in the console:
Uncaught TypeError: Cannot read properties of undefined (reading 'up')

Reason:
Each method (up, down, showStep) does not return any value, so they implicitly return undefined. After the first call, ladder.up() returns undefined, and chaining another .up() results in undefined.up().

Fix:
Return the object itself (this) from each method to enable chaining.

Corrected Example:

let ladder = {
 step: 0,
 up() {
 this.step++;
 return this;
 },
 down() {
 this.step--;
 return this;
 },
 showStep() {
 alert(this.step);
 return this;
 }
};

ladder.up().up().down().showStep().down().showStep(); // works as expected