Add Decimal Input · Build a calculator with vanilla JavaScript

Task

Allow users to create decimal numbers without adding more than one decimal point.

Open

Open:

js/calculator.js

Add an inputDecimal() method inside the Calculator class.

Add the method

javascript

inputDecimal() {
  if (this.state.waitingForOperand || this.state.justCalculated) {
    this.state.current = '0.';
    this.state.waitingForOperand = false;
    this.state.justCalculated = false;
    return;
  }

  if (!this.state.current.includes('.')) {
    this.state.current += '.';
  }
}

The includes('.') check prevents values such as 12.3.4.

Starting with 0. also means a decimal can be entered as the first part of a number.

Test

Run:

javascript

calculator.clear();
calculator.inputDigit('1');
calculator.inputDecimal();
calculator.inputDigit('5');
calculator.state.current;

You should get:

text

"1.5"

Now try:

javascript

calculator.inputDecimal();
calculator.state.current;

The value should still be:

text

"1.5"

Checkpoint

The calculator can now build valid decimal numbers while preventing duplicate decimal points.