Vérifier si une variable est indéfinie ou nulle. JavaScript

#JavaScript #null #typeof #undefined

undefined, null

JavaScript

xxxxxxxxxx
 
function checkVariable(variable) {
​
    if(variable == null) {
        console.log('The variable is undefined or null');
    }
    else {
       console.log('The variable is neither undefined nor null');
    }
}
​
let newVariable;
​
checkVariable(5);
checkVariable('hello');
checkVariable(null);
checkVariable(newVariable);

Output result

The variable is neither undefined nor null
The variable is neither undefined nor null
The variable is undefined or null
The variable is undefined or null

typeof

JavaScript

xxxxxxxxxx
 
function checkVariable(variable) {
​
    if( typeof variable === 'undefined' || variable === null ) {
        console.log('The variable is undefined or null');
    }
    else {
       console.log('The variable is neither undefined nor null');
    }
}
​
let newVariable;
​
checkVariable(5);
checkVariable('hello');
checkVariable(null);
checkVariable(newVariable);

Output result

The variable is neither undefined nor null
The variable is neither undefined nor null
The variable is undefined or null
The variable is undefined or null

JavaScript

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Vérifier si une variable est indéfinie ou nulle. JavaScript

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