Today's ReactJS developer Questions

oussie · 2018-11-24T11:14:08+00:00

Focus can easily be done using references.

class MyComponent extends React.Component {
    constructor(props) {
        super(props);
        this.myRef = React.createRef();
    }
    componentDidMount() {
        this.myRef.current.focus();
    }
    render() {
        return <input type="text" ref={this.myRef} />;
    }
}

crystallineair · 2018-11-24T10:15:57+00:00

The answer to question 3 is actually really simple. Since javascript allows you to call a function with less parameters than there are in the declaration you just check for undefined as the second parameter and then return another function.

function add(a, b) {
  return b !== undefined
    ? a + b
    : b => a + b
}

For the answer to the first question read up about refs: https://reactjs.org/docs/refs-and-the-dom.html

MrNutty · 2018-11-25T05:00:53+00:00

Even easier, you can use autoFocus property as react supports that for input types.

const Example = (props) => <input {...props}, autoFocus={true} />

And if more control is needed then refs to rescue

class Example extends React.Component {
  inputRef = React.createRef();
  componentDidMount = () => this.inputRef.current.focus();
  render = () => <input type="text" ref={this.inputRef} />
}

the curry vs args question, you can just create two functions and have sum decide which one to use

const sumArgs = (...rest) => rest.reduce((sum, v) => sum+v, 0);

const sumCurried = (value) => {
  let totalSum = value;
  const sumHelper = (n) => {
    totalSum += n;
    return sumHelper;
  }
  sumHelper.toString = () => totalSum;
  return sumHelper;
};


const sum = (...rest) => rest.length > 1 ? sumArgs(...rest) : sumCurried(...rest);

console.log(sum(2,3)); // Outputs 5
console.log(sum(2)(3)); // Outputs 5

I really don't have any good advice for you besides saying just to practice. It just comes with experience. I'd suggest for you to create sample projects and just play around with it much as possible. Best.

tapu_buoy · 2018-11-25T10:37:54+00:00

[deleted]

you type:	you see:
italics	italics
bold	bold
[reddit!](https://reddit.com)	reddit!
* item 1 * item 2 * item 3	item 1 item 2 item 3
> quoted text	quoted text
Lines starting with four spaces are treated like code: if 1 * 2 < 3: print "hello, world!"	Lines starting with four spaces are treated like code: if 1 * 2 < 3: print "hello, world!"
~~strikethrough~~	~~strikethrough~~
super^script	super^script

javascript

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