View source for DOM Controls that do things

<pre id='shellbody' data-qtp='clicky'></pre>
==A button==
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When  the user clicks the button the DOM gets changed.
<pre class=usr>
let b = document.createElement('button');
b.innerText = 'click me';
b.onclick = ()=>{
  document.body.append('Hello world');
}
document.body.append(b);
</pre>
<pre class=ans>
let b = document.createElement('button');
b.innerText = 'click me';
b.onclick = ()=>{
  document.body.append('Hello World!');
}
document.body.append(b);
</pre>
</div>

==An input box and a button==
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The user can change the text that gets echoed.
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let i = document.createElement('input');
i.value = 'New York ';
let b = document.createElement('button');
b.innerText = 'click me';
b.onclick = ()=>{
  document.body.append(i.value);
}
document.body.append(i,b);
</pre>
<pre class=ans>
let i = document.createElement('input');
i.value = 'New York ';
let b = document.createElement('button');
b.innerText = 'click me';
b.onclick = ()=>{
  document.body.append(i.value);
  document.body.append(i.value);
}
document.body.append(i,b);
</pre>
</div>

==Change Color==
An '''input''' element can be a text box.
*In this example the text box is created and given a default value
*The user can change that value.
*The button text should get changed to the color of the moment. You can do that with the line:
  b.style.color = i.value;

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<pre class=usr>
let i = document.createElement('input');
i.value = 'green';
let b = document.createElement('button');
b.innerText = 'click me';
b.onclick = ()=>{
}
document.body.append(i,b);
</pre>
<pre class=ans>
let i = document.createElement('input');
i.value = 'green';
let b = document.createElement('button');
b.innerText = 'click me';
b.onclick = ()=>{
  b.style.color = i.value;
}
document.body.append(i,b);
</pre>
</div>

==Do some maths==
An '''input''' element can be a text box.
*You can turn a string into a number with the parseInt function

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<pre class=usr>
let i = document.createElement('input');
i.value = 21;
let b = document.createElement('button');
b.innerText = 'click to double';
b.onclick = ()=>{
  let r = document.createElement('div');
  r.innerText = parseInt(i.value) + 1;
  document.body.append(r);
}
document.body.append(i,b);
</pre>
<pre class=ans>
let i = document.createElement('input');
i.value = 21;
let b = document.createElement('button');
b.innerText = 'click to double';
b.onclick = ()=>{
  let r = document.createElement('div');
  r.innerText = parseInt(i.value) * 2;
  document.body.append(r);
}
document.body.append(i,b);
</pre>
</div>