DOM Controls that do things

A button

When the user clicks the button the DOM gets changed.

let b = document.createElement('button');
b.innerText = 'click me';
b.onclick = ()=>{
  document.body.append('Hello world');
}
document.body.append(b);

let b = document.createElement('button');
b.innerText = 'click me';
b.onclick = ()=>{
  document.body.append('Hello World!');
}
document.body.append(b);

An input box and a button

The user can change the text that gets echoed.

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);

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);

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;

let i = document.createElement('input');
i.value = 'green';
let b = document.createElement('button');
b.innerText = 'click me';
b.onclick = ()=>{
}
document.body.append(i,b);

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);

Do some maths

An input element can be a text box.

• You can turn a string into a number with the parseInt function

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);

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);

Pick colours from a drop down

• Set the document.body.style.background

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);

let i = document.createElement('select');
i.append(...['red','blue','yellow']
  .map(c=>{
    let o = document.createElement('option');
    o.innerText = c;
    return o;
  }))
let b = document.createElement('button');
b.innerText = 'click me'
b.onclick = ()=>{
  document.body.style.background = i.value;
}
document.body.append(i,b);