git clone this repo to start the calculator homework.

You can open calculator.html to see the (nonfunctional) calculator page. You're gonna make it work!

Try the following before jumping to the solution. Note this lab will require lots of code repetition. We aren't writing clean code. We will write a very rough draft of code that you can later clean up.

1. The calculator.js file is linked in the calculator.html, but you won't be able to manipulate the page before the window loads. Write a function to handle the window.onload
   • The window.onload handler should alert("loaded")
   • Use a selector to grab each div that is a number button using the id. Note: this is highly repetitive and will require 9 selector statements.
   • Add an onclick listener to each button and alert a message with which one number is clicked.

==========

Solution:

  window.onload = function () {
  	alert("Window loaded!");
  	var buttons = document.querySelectorAll(".button");
  		
	// Grab number buttons
	var numOne = document.getElementById("number_1"),
	    numTwo = document.getElementById("number_2"),
	    numThree = document.getElementById("number_3");
	    // and so on
	 
	// alert which num was clicked
	numOne.onclick = function () {
		alert("1");
	};
	
	numTwo.onclick = function () {
		alert("2");
	};
	
	numThree.onclick = function () {
		alert("3");
	}
  };

==========

• Modify the calculator.html so that each operation button, +, -, *, / has an id that can be used to select it.
• Select each operation button from the DOM using their above ids.
• Add an onclick listener onto each operation button that alerts which operation was clicked

==========

Solution:

window.onload = function () {
  	alert("Window loaded!");
  	var buttons = document.querySelectorAll(".button");
  		
	// Grab number buttons
	var numOne = document.getElementById("number_1"),
	    numTwo = document.getElementById("number_2"),
	    numThree = document.getElementById("number_3");
	    // and so on
	 
	// alert which num was clicked
	numOne.onclick = function () {
		alert("1");
	};
	
	numTwo.onclick = function () {
		alert("2");
	};
	
	numThree.onclick = function () {
		alert("3");
	}
	
	
	// if you had id's like the following:
	var addOp = document.getElementById("op_plus"),
	   subOp = document.getElementById("op_sub"),
	   multOp = document.getElementById("op_mult"),
	   divOp = document.getElementById("op_div"),
	   entOp = document.getElementById("op_ent"),
	   clrOp = document.getElementById("op_clr");
	   
	// add click listeners to each operation
	addOp.onclick = function () {
		alert("+");
	};

	subOp.onclick = function () {
		alert("-");
	};
	
	multOp.onclick = function () {
		alert("*");
	};

	divOp.onclick = function () {
		alert("/");
	};
	
	// also add them to calculator operations
	entOp = function () {
		alert("enter pushed");
	}
	clrOp = function () {
		alert("clear pushed");
	}
};

==========

• Like how you selected numbers and operations earlier so that you could manipulate them and listen to them for clicks, you now want to select the display div. In particular, you need to select #result_display_value.

• Now go back and modify your number click listeners to not just alert, but also, they should concat it onto the innerHTML of the #result_display_value div.

   	Imagine an empty display
   	
   	 -----------
       |			|
        ----------
        
       You click 1
       
   	 -----------
       |		1	| and it shows up 
        ----------    
       
       You click 2 after
   	 -----------
       |		12	| it displays says 12
        ----------	    
       
  

====== Solution will be coded together... CODE ALONG! :D

======

Thus far we've left our calculator with a number being input in the display, 123. If someone pushes an operation you then need to clear the screen, and display the operation somewhere a user can remember it. You should display the operation pushed in the div with id operator_display.

```
	Enters a number
	 -----------
    |		123	| 
     ----------	
     
    Pushes +
	 -----------
    |			| clears the display first
     ----------	
     
	 -----------
    |+			| then display shows the operation
     ----------		    	    
    
    
```

With the ability to enter one number onto the screen and then press an operation we cleared out the display. We should save the first number in a variable somewhere, so it isn't lost.

Modify your work from stage three to add the following features when someone enters an operation:

• Save the first number input to the display in a variable called first when someone pushes an operation.
• Save the operation in a variable called op.

When someone starts entering their second number you don't have to worry about losing any information and you can just display it.

• When a user clicks the enter button use the last value and the number currently in the display to perform the operation stored in op.
• Use the result calculated above and display it in the #result_display_value.
• Once you have the result above clear out the #operator_display.