I've made a program that allows a user to write text on a "white board" and change color in real time. I'm now trying to give the user the ability to change font-size as well. How could I combine the "writing_size" variable with the characters "px" to form a value for "font-size"?
<!DOCTYPE html>
<html>
<head>
<link rel="stylesheet" type="text/css" href="style.css">
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.6.9/angular.min.js"></script>
<title>AngularJS Whiteboard</title>
</head>
<body>
<div ng-app="">
<textarea name="message" rows="10" cols="30" ng-model="writing">
</textarea>
<span> Marker color: <input type = "text" size = "7" ng-model="marker_color"></span>
<span> Writing size: <input type = "text" size = "7" ng-model="writing_size"></span>
<br>
<br>
<div id = "whiteboard" ng-bind="writing" ng-style="{ color : marker_color, font-size: {{writing_size + 'px'}} }">
</div>
<div id = "test">
{{ writing_size + "px"}}
</div>
</div>
</body>
</html>
First problem: the font-size key must not be used without apostrophes, becuase it is not a valid JS Object key. You need to write e.g. ng-style="{'font-size': '12px'}".
Secondly, ng-style attribute is being evaluated as JS, so you can't use the double curly braces syntax, because it is not a valid JS. Just write like you would inside JS: ng-style="{'font-size': writing_size + 'px'}".
Your working example:
<!DOCTYPE html>
<html>
<head>
<link rel="stylesheet" type="text/css" href="style.css">
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.6.9/angular.min.js"></script>
<title>AngularJS Whiteboard</title>
</head>
<body>
<div ng-app="">
<textarea name="message" rows="10" cols="30" ng-model="writing">
</textarea>
<span> Marker color: <input type = "text" size = "7" ng-model="marker_color"></span>
<span> Writing size: <input type = "text" size = "7" ng-model="writing_size"></span>
<br>
<br>
<div id = "whiteboard" ng-bind="writing" ng-style="{ color : marker_color, 'font-size': writing_size + 'px' }">
</div>
<div id = "test">
{{ writing_size + "px"}}
</div>
</div>
</body>
</html>