typeof Operator with Assignment in JavaScript – A Publicis Sapient Interview Question. Javascript interview prepratiron.

Understanding the Code Step by Step

The given JavaScript snippet involves variable assignment and the typeof operator. Let’s analyze how JavaScript processes it.

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Javascript Code:

var z = 1, y = z = typeof y;
console.log(y);

Step 1: Breaking Down Variable Declarations

var z = 1;

• Here, z is declared and assigned the value 1.

y = z = typeof y;

• The key part here is right-to-left assignment (= assigns values from right to left).
• We evaluate typeof y first and then assign the result to z, and then assign z to y.

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Step 2: Evaluating typeof y

• At this point in execution, y has not been explicitly assigned a value, so it is undefined.
• The typeof operator returns a string representation of the data type.

typeof y; // "undefined"

Step 3: Assigning the Value

z = typeof y; // z = "undefined"
y = z;        // y = "undefined"

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Step 4: Logging the Output

console.log(y);

Since y is now "undefined" (a string), the output is:

"undefined"

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Final Output

"undefined"

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Remember key points:

1. Assignment (=) in JavaScript happens from right to left.
2. typeof always returns a string, even when checking undefined.
3. Variables declared with var are hoisted, meaning y exists but is undefined before assignment.
4. The final value of y is "undefined" (a string), not undefined (a primitive type).

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✔ Final Answer:

B) undefined

This question appeared in the Publicis Sapient 2nd round of interview, testing the candidate’s knowledge of assignment operator (=) and typeof operator in JavaScript.