How Does Operator Precedence Impact JavaScript\'s Ternary Operator?

Understanding Operator Precedence in JavaScript's Ternary Operator

When dealing with JavaScript's ternary operator, it's crucial to grasp operator precedence to ensure the code executes as intended. In the given example, the confusion stems from the combination of the ternary operator with the assignment operator.

Interpreting the Code

The provided code:

<code class="javascript">h.className += h.className ? ' error' : 'error'</code>

is not syntactically correct in JavaScript. The left-hand side of the assignment operator, h.className, is already an expression, so attempting to apply another operator directly to it would result in an error.

The Correct Syntax

To have the code execute without errors, it should be rewritten as:

<code class="javascript">h.className = h.className + (h.className ? ' error' : 'error')</code>

In this case, the parentheses enclose the entire ternary operation, ensuring that its result is assigned to h.className. This is crucial because the ternary operator has a lower precedence than the assignment operator.

Operator Precedence

Operator precedence defines the order in which operators are evaluated in a code expression. In JavaScript, the ternary operator (?:) has a lower precedence than the assignment operator (=), meaning that the ternary operation will be executed before the assignment.

Therefore, when the above code is executed correctly, it checks if h.className is already set. If it is, it adds ' error' to the existing value; otherwise, it assigns 'error' as the value for h.className.

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