The ternary operator is a nice way to write concise value assignments without having to write a more lengthy if/else.
For example:

// This...
let value;
if (test) value = 1;
else valeu = 2;

// can be written as this:
const value = test ? 1 : 2;

However it's easy to misuse the ternary operator for things where simpler operators could often have been a better choice. So here are some alternatives for common mistakes.

Static true/false assignments:

const value = test ? true : false;
// can be replaced by boolean casting:
const value = !!test;
// or even
const value = Boolean(test); // I prefer the shorter alternative

Nullable assignment (falsy case)

const value = test ? test : null;
// can be written like this
const value = test || null;

Note: The code above will return null as long as test is falsy.

Nullable assignment (nullish case)

const value = test !== null || test !== undefined ? test : null;
// can be written like this:
const value = test ?? null;

See: Nullish coalescing operator (??)

By the way...

const test = a === null || a === undefined;
// can be simplified as:
const test = a == null;

Checking for undefined

I have seen this a few times. I promise.

const value = obj ? obj.a : undefined;
// which can simply be:
const value = obj && obj.a;
// or in more recent implementations:
const value = obj?.a;

See: Optional chaining (?.) [elvis operator]

Beware of browser coverage. If you want to use optional chaining safely, it might be a good idea to use TypeScript configured to transpile the code to ES5 with the modules configured to esnext, to use the latest ECMAScript features.

The ternary (but not actually ternary) operator

This is my favorite one, and also an honest mistake. Some people get overexcited with the simplicity of the ternary operator and might think it is just a "shorter" if/else statement.

let value;
test ? value = 8 : null;
// when they meant 
if (test) value = 8;

The single-line if statement is simple and clean enough for that purpose, and we know test ? value = 8 will not work. The ternary operator needs to have an else return value. If you don't need it, use a single-line if.

Another variant

In React, sometimes when we want to render a component if a specific condition is true, we might see something like this.

{ myCondition ? <MyComponent /> : null }
// when they meant 
{ myCondition && <MyComponent /> }

I would only use a ternary operator for the example below in the case I want to render one component or another.

Wrapping up...

In a nutshell, if your ternary operator does not have a structure like the one below, you should raise an eyebrow and check if there really aren't other simpler alternatives.

const value = test ? otherValue : anotherValue;

Can you think of other examples you have seen of poor use of the ternary operator? Please let me know in the comments below.