score:4

Accepted answer

Your JSX of

<div id={condition ? 'msg' : null}>Hello World!</div>

which is not valid Javascript by itself, will be compiled into the following ReactJS call:

React.createElement(
  'div',                            // Element "tag" name.
  { id: condition ? 'msg' : null }, // Properties object.
  'Hello World!'                    // Element contents.
);

which is valid Javascript, ready to be interpreted/compiled by your Javascript runtime environment. As you can see, there is no way to jam an if-else into that statement, as it cannot be compiled into valid Javascript.


You could instead use an immediately-invoked function expression and pass the value returned from within:

<div id={(function () {
    if (condition) {
        return "msg";
    } else {
        return null;
    }
})()}>Hello World!</div>

which will compile into the following valid Javascript:

React.createElement(
    "div",
    {
        id: (function () {
            if (condition) {
                return "msg";
            } else {
                return null;
            }
        })()
    },
    "Hello World!"
);

score:1

// This JSX:
<div id={if (condition) { 'msg' }}>Hello World!</div>

// Is transformed to this JS:
React.createElement("div", {id: if (condition) { 'msg' }}, "Hello World!");

So, you see if/else does not fit in this model. Better to use it outside of jsx. may be in render function.

score:2

if-else statements don't work inside JSX. This is because JSX is just syntactic sugar for function calls and object construction. React Docs


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