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Node.js - assert.strictEqual() Function

The assert module provides a set of assertion functions for verifying invariants. The Node.js assert.strictEqual() function is an inbuilt function of the assert module of Node.js.

The Node.js strictEqual() function is used to determine if two values are equal using a stricter comparison than the == operator. This function compares both the data type and value of two variables or objects and returns true only if they are exactly the same. Also, comparing NaN (Not-A-Number) to any other value, including itself, returns false.

This function will test equality on both of its parameters actual and expected. Whenever both the parameters are similar, the function doesn't throw AssertionError. If both the parameters are not similar, then it will throw an AssertionError to the output. This function is an alias of Node.js assert.deepStrictEqaul() function.

Syntax

Following is the syntax of Node.js assert.strictEqaul() function −

assert.strictEqual(actual, expected[, message]);

Parameters

This function accepts three parameters. The same are described below.

  • actual − (required) The value passed in this parameter will be evaluated. The value can be of any type.

  • expected − (required) The value passed in this parameter will be compared to the actual value. The value can be of any type.

  • message − (optional) String or Error type can be passed as an input into this parameter.

Return Value

This function will return the AssertionError on the terminal if both actual and expected are not matched.

Example

In the following example, we are passing two identical integers to the actual and expected parameters of the Node.js assert.strictEqual() function.

const assert = require('assert');
var num1 = 45;
var num2 = 45;
assert.strictEqual(num1, num2, 'Both the values are same');

Output

If we compile and run the code, No AssertionError will be thrown to the output. This is true because 45 == 45.

// Returns nothing

Example

In the following example, we are passing two distinct integers to the actual and expected parameters of the function.

const assert = require('assert');
var int1 = 34;
var int2 = 10;
assert.strictEqual(int1, int2, 'Both the values are not same');

Output

If we compile and run the code, it will throw AssertionError to the output along with the text in message parameter. This is false because 34 !== 10.

assert.js:79
   throw new AssertionError(obj);
   ^

AssertionError [ERR_ASSERTION]: Both the values are not same
   at Object.<anonymous> (/home/cg/root/639c3f570123e/main.js:5:8)
   at Module._compile (internal/modules/cjs/loader.js:702:30)
   at Object.Module._extensions..js (internal/modules/cjs/loader.js:713:10)
   at Module.load (internal/modules/cjs/loader.js:612:32)
   at tryModuleLoad (internal/modules/cjs/loader.js:551:12)
   at Function.Module._load (internal/modules/cjs/loader.js:543:3)
   at Function.Module.runMain (internal/modules/cjs/loader.js:744:10)
   at startup (internal/bootstrap/node.js:238:19)
   at bootstrapNodeJSCore (internal/bootstrap/node.js:572:3)

Example

In the following example, we are passing two identical strings to the actual and expected parameters of the function.

const assert = require('assert');
var text1 = 'Welcome to India';
var text2 = 'Welcome to India';
assert.strictEqual(text1, text2, 'Both the strings are identical');

Output

If we compile and run the code, No AssertionError will be thrown to the output. This is true because text1 == text2.

// Returns nothing

Example

In the following example, we are passing two string values and checking their type.

const assert = require('assert');
var text1 = 'Rise';
var text2 = 'Rule';
assert.strictEqual(typeof text1 === 'string', typeof text2 === 'number', 'Both the strings are not identical');

Output

If we compile and run the code, it will throw an AssertionError along with the text in the message to the output. This is false because 'text2' == 'number'.

assert.js:79
   throw new AssertionError(obj);
   ^
   
AssertionError [ERR_ASSERTION]: Both the strings are not identical
   at Object.<anonymous> (/home/cg/root/639c3f570123e/main.js:6:8)
   at Module._compile (internal/modules/cjs/loader.js:702:30)
   at Object.Module._extensions..js (internal/modules/cjs/loader.js:713:10)
   at Module.load (internal/modules/cjs/loader.js:612:32)
   at tryModuleLoad (internal/modules/cjs/loader.js:551:12)
   at Function.Module._load (internal/modules/cjs/loader.js:543:3)
   at Function.Module.runMain (internal/modules/cjs/loader.js:744:10)
   at startup (internal/bootstrap/node.js:238:19)
   at bootstrapNodeJSCore (internal/bootstrap/node.js:572:3)

Example

In the following example, we are passing two different string values and not passing any text to the message parameter.

const assert = require('assert');
assert.strictEqual('RRR', 'ZZZ');

Output

If we compile and run the code, it will throw an AssertionError to the output and a default message will be assigned by the function.

assert.js:79
   throw new AssertionError(obj);
   ^
   
AssertionError [ERR_ASSERTION]: Input A expected to strictly equal input B:
+ expected - actual
   
- 'RRR'
+ 'ZZZ'
   at Object.<anonymous> (/home/cg/root/639c3f570123e/main.js:3:8)
   at Module._compile (internal/modules/cjs/loader.js:702:30)
   at Object.Module._extensions..js (internal/modules/cjs/loader.js:713:10)
   at Module.load (internal/modules/cjs/loader.js:612:32)
   at tryModuleLoad (internal/modules/cjs/loader.js:551:12)
   at Function.Module._load (internal/modules/cjs/loader.js:543:3)
   at Function.Module.runMain (internal/modules/cjs/loader.js:744:10)
   at startup (internal/bootstrap/node.js:238:19)
   at bootstrapNodeJSCore (internal/bootstrap/node.js:572:3)

Example

In the following example below, we are not passing any input values to the actual, expected, and message parameters of the function.

const assert = require('assert');
assert.strictEqual();

Output

// Returns Nothing

Note − Sometimes online compiler may not give us the expected result, so we are executing the above code locally.

If we compile and run the code, the function will throw an AssertionError along with the default message "The 'actual' and 'expected' arguments must be specified" to the output.

node:assert:568
   throw new ERR_MISSING_ARGS('actual', 'expected');
   ^
   
TypeError [ERR_MISSING_ARGS]: The "actual" and "expected" arguments must be specified
   at new NodeError (node:internal/errors:387:5)
   at Function.strictEqual (node:assert:568:11)
   at Object.<anonymous> (C:\Users\Lenovo\Desktop\JavaScript\nodefile.js:3:8)
   at Module._compile (node:internal/modules/cjs/loader:1126:14)
   at Object.Module._extensions..js (node:internal/modules/cjs/loader:1180:10)
   at Module.load (node:internal/modules/cjs/loader:1004:32)
   at Function.Module._load (node:internal/modules/cjs/loader:839:12)
   at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
   at node:internal/main/run_main_module:17:47 {
   code: 'ERR_MISSING_ARGS'
}
nodejs_assert_module.htm
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