refactor code to use functions and switch cases

[AmeliaES]

javaScriptCalculator/calculator.html

Lines 80 to 143 in 50319ac

	if(numbers.has(inputField.currentValue)) {
	// Starting a new calculation
	if(inputField.display === ' ' || equals.has(inputField.previousValue)) {
	// Update display with the number clicked
	inputField.display = inputField.currentValue;
	// Update the string to evaluate
	inputField.stringToEval = inputField.currentValue;
	// Appending a number to a current calculation, when previous button is an operator
	} else if (operators.has(inputField.previousValue)) {
	// Update the display with current number
	inputField.display = inputField.currentValue;
	// Update the string to evaluate
	inputField.stringToEval += inputField.currentValue;
	// Append number to string to make a multi digit number
	} else if (numbers.has(inputField.previousValue) || decimal.has(inputField.previousValue)) {
	// Append the number clicked to the display
	inputField.display += inputField.currentValue;
	inputField.stringToEval += inputField.currentValue;
	}
	} else if(operators.has(inputField.currentValue)) {
	// - **Operators**: if a user clicks on an operator:
	// - append that operator to the string to evaluate only when the previous value is a number (not a decimal)
	// - however the display should not change, the previous number should stay the same at this point
	// - if the user clicks on the operator multiple times, ie ++++_*/ one after another then replace the last character (an operator character) with the operator that was last clicked.
	if(operators.has(inputField.previousValue)) {
	// Replace the last operator with the current operator
	inputField.stringToEval = inputField.stringToEval.slice(0, -1) + inputField.currentValue;
	} else if(numbers.has(inputField.previousValue) || equals.has(inputField.previousValue)) {
	// Append the operator to the string to evaluate
	inputField.stringToEval += inputField.currentValue;
	}
	} else if(decimal.has(inputField.currentValue)) {
	// - **Decimal**: if a user clicks on decimal:
	// - append a decimal to string
	// - but only if the previous value is a number
	// - and not if there is already a decimal in the string
	if( (numbers.has(inputField.previousValue) || equals.has(inputField.previousValue)) && !inputField.display.includes('.')) {
	// Append the decimal to the display
	inputField.display += inputField.currentValue;
	// Append the decimal to the string to evaluate
	inputField.stringToEval += inputField.currentValue;
	}
	} else if(clear.has(inputField.currentValue)) {
	// - **Clear**: if a user clicks on clear:
	// - replace the display with "0"
	// - replace the string to evaluate with null
	inputField.display = ' ';
	inputField.stringToEval = null;
	} else if(equals.has(inputField.currentValue)) {
	// - **Equals**: if a user clicks on equals:
	// - evalulate that string
	// - but only evaluate if the last character is a number, it cannot be a "." or an operator character.
	// - replace the display with the result of the evaluation
	if (numbers.has(inputField.previousValue)) {
	// Evaluate the string
	inputField.display = eval(inputField.stringToEval).toString();
	// Update the string to evaluate
	inputField.stringToEval = inputField.display;

This code is not easy to read and not easy to maintain.
Improve by making helper functions and using switch cases.