The ifError method of the assert module in Node.js throws an error if the provided value is not null or undefined. The ifError method is commonly used to test error arguments in callbacks.
The process is illustrated below:
To use the ifError method, you will need to install the assert module using the command prompt, as shown below:
npm install assertAfter the installation is complete, you will need to import the assert module into the program, as shown below:
const assert = require('assert');The prototype of the ifError method is shown below:
ifError(value)Paramaters
The ifError method takes a single mandatory parameter that represents the value to be checked for an error.
Return value
If value is not null or undefined, then the ifError method throws an AssertionError, and the program terminates; otherwise, execution continues as normal.
Example
The code below shows how the ifError method works in Node.js:
const assert = require('assert');
// evaluating first expression
try{
assert.ifError('23')
console.log("No error.")
}
catch(error){
console.log(error.message)
}
// evaluating second expression
try{
assert.ifError('error')
console.log("No error.")
}
catch(error){
console.log(error.message)
}
// evaluating third expression
try{
assert.ifError(null)
console.log("No error.")
}
catch(error){
console.log(error.message)
}
// evaluating fourth expression
try{
assert.ifError(undefined)
console.log("No error.")
}
catch(error){
console.log(error.message)
}
Explanation
The code above uses 4 different expressions to show the behavior of the ifError method.
In the first two expressions in lines 5 and 14, value is “23” and “error”, respectively. Since value is neither null nor undefined, the ifError method throws an error, which triggers the catch branch of the try-catch block. The code outputs the message associated with the error, i.e., the value parameter itself.
In the expressions in line 23 and 32, value is null and undefined, respectively. Therefore, the ifError method does not throw any errors, and only the try branch of the try-catch block executes.
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