backup

js_workshop7/index.js

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+// Creates the Calculator Object
+function Calculator() {
+    // Set current and buffer values to 0
+    this.current = 0;
+    this.buffer = "0";
+    // Set previous operator to null
+    this.previousOperator = null;
+    // When button is clicked, if not a number, buffer an operator
+    // if a number, buffer the operand.
+    this.buttonClicked = ( value ) => {
+        if (isNaN(parseInt(value))) {
+            calculator.bufferOperator(value);
+        } else {
+            calculator.bufferOperand(value);
+        }
+        // Push to value
+        this.renderResult();
+    }
+    // Function to buffer an operator given a value
+    this.bufferOperator = (value) =>
+    {
+        switch( value ) {
+            // If the value is Clear, reset all values to default.
+            case "C":
+                this.buffer = "0";
+                this.current = 0;
+                this.previousOperator = null;
+                break;
+            // If the value is equals, set previous operator to null,
+            // flush the operation using the typecasted buffer, and set
+            // buffer to the current value in order to continue operations.
+            // Finally set current value and previous operator to default.
+            case "=":
+                if( this.previousOperator === null ) {
+                    return;
+                }
+                this.flushOperation( parseInt( this.buffer ));
+                this.buffer = "" + this.current;
+                this.previousOperator = null;
+                this.current = 0;
+                break;
+            // If value is backspace, delete the last digit in the buffer.
+            case "←":
+                if( this.buffer.length === 1 ) {
+                    this.buffer = 0;
+                }
+                else {
+                    this.buffer = this.buffer.substring( 0, this.buffer.length - 1 );
+                }
+                break;
+            default:
+                this.calculate( value );
+        }
+    }
+    // Adds operand, given a value, to the buffer.
+    this.bufferOperand = ( value ) =>
+    {
+        if( this.buffer === "0" )
+        {
+            this.buffer = value;
+        }
+        else
+        {
+            this.buffer += value;
+        }
+    }
+    // Performs operator functions depending on which operator was clicked.
+    // Given a tempBuffer, perform the corresponding operation to the current value.
+    this.flushOperation = ( tempBuffer ) => {
+        if( this.previousOperator === "+" ) { this.current += tempBuffer}
+        else if( this.previousOperator === "-" ) { this.current -= tempBuffer}
+        else if( this.previousOperator === "x" ) { this.current *= tempBuffer}
+        else { this.current /= tempBuffer}
+    }
+    // Given a value, create a temporary buffer equal to current buffer,
+    // perform the corresponding operation, and reset operator and buffer to
+    // default values.
+    this.calculate = ( value ) => {
+        const tempBuffer = parseInt( this.buffer );
+        if ( this.current === 0 ) {
+            this.current = tempBuffer;
+        }
+        else {
+            this.flushOperation(tempBuffer)
+        }
+        this.previousOperator = value;
+        this.buffer = "0";
+    }
+    // Exclusively called when a button is clicked, display a value
+    // rounded to 4 decimal places in the result box.
+    this.renderResult = () => {
+        // Note: this is the proper way to round to decimal places. Math.round( ( x * 100 ) / 100 )
+        // will almost always give rounding errors
+        result.value = +(Math.round(this.buffer + 'e+4') + 'e-4');
+    }
+}
+
+// Instantiate Calculator
+let calculator = new Calculator();
+
+// Create constant for result display HTML object
+const result = document.querySelector("#result");
+
+// Create Event Listener for button
+document.querySelector( '.buttons' ).addEventListener( 'click', function( event ) {
+    // Pass the value of the HTML button to the buttonClicked() function.
+    calculator.buttonClicked( event.target.innerHTML );
+});