Items function in JavaScript for looping over dictionaries like Python

23 February 2018   1 comment   ReactJS, JavaScript

Too many times I've written code like this:

class MyComponent extends React.PureComponent {
  render() {
    return <ul>
      {Object.keys(this.props.someDictionary).map(key => {
        return <li key={key}><b>{key}:</b> {this.props.someDictionary[key]}</li> 
      })}
    </ul>
  }
}

The clunky thing about this is that you have to reference the dictionary twice. Makes it harder to refactor. In Python, you do this instead:

for key, value in some_dictionary.items():
    print(f'$key: $value')

To do the same in JavaScript make a function like this:

function items(dict, fn) {
  return Object.keys(dict).map((key, i) => {
    return fn(key, dict[key], i)
  })
}

Now you can use it "more like Python":

class MyComponent extends React.PureComponent {
  render() {
    return <ul>
      {items(this.props.someDictionary, (key, value) => {
        return <li key={key}><b>{key}:</b> {value}</li> 
      })}
    </ul>
  }
}

Example on CodeSandbox here

UPDATE

Thanks to @Osmose and @saltycrane for alerting me to Object.entries().

class MyComponent extends React.PureComponent {
  render() {
    return <ul>
      {Object.entries(this.props.someDictionary).map(([key, value]) => {
        return <li key={key}><b>{key}:</b> {value}</li> 
      })}
    </ul>
  }
}

Updated CodeSandbox here

Comments

Mike Lane

Your python example is a little bit wrong. It should be this:

```python
for key, value in some_dictionary.items():
    print(f'{key}: {value}')
```

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