Not sure exactly what you mean, but maybe this help?

<Row>
  {elt.client ? elt.client.libelle : elseStatement}
</Row>

Meaning: `if (elt.client) { return elt.client.libelle } else { return "whatever else you want" }

`

You can make use of ternary operator (? and : ). This operator is frequently used as an alternative to an if...else statement.

<Row>
 { elt?.client?.libelle ? ("Client : " + elt.client.libelle) : "" }
</Row>

It takes three operands: a condition followed by a question mark (?), then an expression to execute if the condition is truthy followed by a colon (:), and finally the expression to execute if the condition is falsy.

Also, you can utilise optional chaining (?.) operator of JavaScript which prevents an error if a reference is nullish (null or undefined).

In this case, if elt is undefined, it won't throw error. Hence, if all elt, elt.client and elt.client.libelle is defined and the value is no null, "Client : " + elt.client.libelle will display.