Javascript conditional in template string

Question

Is there a way to do conditional within a template string?

For example:

let x, y;

x = ...
y = ...

let templateString = `${x} ${y}`;

I don't want the space in the template string after x to be output if y is undefined. How would I achieve that with template string?

Is this the only way to do it?

 let templateString = `${x}${y ? ' ' + y : ''}`;

Answer 1

What about

let x,y;

const templateString = [x,y].filter(a => a).join(' ');

What it does that it first puts your properties into an array [].

Then it filters the undefined items.

The last it creates a string of the array, by using join with a space.

This way either x or y can be undefined.

Answer 2

如果您不在模板中添加逻辑，看起来会更容易阅读：

let templateString = y ? `${x} ${y}` : `${x}`;

Answer 3

使用嵌套模板文字的另一种稍微简洁的方法。

`${x}${y ? ` ${y}` : ''}`

Answer 4

It's probably overkill for this small example, butTagged template functions provide a nice general solution that allow an amazing amount of flexibility while keeping your template strings clean. For example here's one that will remove text preceding an undefined variable in general:

 function f(str ,...variables){ return variables.reduce((res, v, i) => v ? res + str[i] + v: res, '') } let x, y, z; x = "test" y = "test2" // both defined console.log(f`${x} + ${y}`) // only one: console.log(f`${x} + ${z}`) // random text: console.log(f`${x} with ${z} and ${y}`)

Since it passes everything to a function, you can do almost any logic you want while still having readable strings. There's some documentation about halfway down the MDN Page on template literals .

Answer 5

technically you can nest these template strings, its not pretty but this works

let templateString = `${y ? `${x} ${y}`: `${x}`}`;

i would use the solution from the first comment though.

Answer 6

You can also use functions inside expressions

Here is an example of it

 let x, y; x = 'test' y = undefined; let templateString = `${x} ${y}`; function fn(value1,value2) { return value2? (value1 + ' ' + value2) : value1 } console.log('when undefined =',`${fn(x,y)}`); x = 'test' y = 'test1'; console.log('when not undefined = ',`${fn(x,y)}`);

reference

Answer 7

甚至更好

const templateString = `${x} ${y}`.trim();