JavaScript Type Coercion Explained. What Happens When You Add Boolean and Number or String. Data Type Magic in JavaScript. Boolean Numbers and Strings Interaction Explained

Lets explain the Code:

console.log(true + 1);
console.log(true + "1");

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Step 1: console.log(true + 1);

What is Happening:

Here, you are adding a boolean value true to a number 1.

JavaScript Type Coercion (Automatic Type Conversion):

When using the + operator, JavaScript automatically converts operands to compatible types based on the context.

When adding:

• Boolean + Number → Boolean is coerced to a number.

 Coercion Rule:

• true becomes 1
• false becomes 0

Calculation:

true + 1 → 1 + 1 → 2

Console Output:

2

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Step 2: console.log(true + "1");

What is Happening:

Here, you are adding a boolean value true to a string "1".

JavaScript Type Coercion:

When using the + operator:

• If any operand is a string, JavaScript performs string concatenation.

Coercion Rule:

• true is converted to the string "true"

Calculation:

true + "1" → "true" + "1" → "true1"

Console Output:

true1

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JavaScript Type Coercion Summary:

Expression	Coercion Type	Result
true + 1	Number	2
true + "1"	String	"true1"

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Why This Happens:

• In true + 1: Both operands are treated as numbers → arithmetic addition.
• In true + "1": One operand is a string → string concatenation happens.

Type Conversion Rules:

1. If either operand is a string → string concatenation happens.
2. If both operands are numbers (or coerced to numbers) → numeric addition happens.

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Quick Real-World Example:

console.log(false + 5);    // Output: 5 → false is treated as 0
console.log(false + "5");  // Output: "false5" → string concatenation

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Final Key Takeaways:

• JavaScript automatically converts types based on the operator and the types of operands.
• + is the only operator that behaves differently: it can mean addition or string concatenation.
• Boolean values:
• true → 1
• false → 0
• When a string is involved, everything is converted to a string.

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✔ Final Answer:

B) 2 true1

This question appeared in the HCL Tech 2nd round of interview, testing the candidate’s knowledge of type coercion when use + operator between boolean, string and number in JavaScript.