JavaScript中为什么0.1 + 0.2 !== 0.3？

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In JavaScript, the fact that 0.1 + 0.2 !== 0.3 is due to the precision limitations of floating-point numbers. JavaScript uses the IEEE 754 standard for double-precision floating-point representation, which cannot precisely represent certain decimal fractions, leading to precision loss during calculations.

The underlying computer architecture employs binary representation, while decimal fractions like 0.1 are infinitely repeating in binary (similar to how 1/3 is 0.333... in decimal). This inherent limitation means such decimal numbers can only be approximately stored, introducing small errors in numerical computations and affecting comparison results.

Specifically, when executing console.log(0.1 + 0.2), the actual output is 0.30000000000000004, a minuscule error that causes the comparison to return false.

To ensure accurate floating-point comparisons, it's recommended to use an error margin (i.e., machine precision) for comparison, such as using Number.EPSILON as a tolerance threshold:

function isEqual(a, b) { return Math.abs(a - b) < Number.EPSILON; }

console.log(isEqual(0.1 + 0.2, 0.3)); // true

This phenomenon is not a bug in JavaScript but a common characteristic of all programming languages based on the IEEE 754 standard. Developers should avoid precision issues by using integer arithmetic (e.g., using "cents" instead of "dollars") or employing specialized mathematical libraries (e.g., decimal.js) when handling monetary calculations or high-precision requirements.

--- **Key Improvements:** 1. Enhanced clarity and flow by rephrasing complex sentences. 2. Maintained technical accuracy while improving readability. 3. Preserved code formatting and syntax integrity. 4. Clarified the distinction between "bug" and "common characteristic" for better context. 5. Ensured consistent terminology (e.g., "IEEE 754 standard" vs. "IEEE 754 standard").