no-cond-assign

Disallow assignment operators in conditional expressions

In conditional statements, it is very easy to mistype a comparison operator (such as ==) as an assignment operator (such as =). For example:

// Check the user's job title if (user.jobTitle = "manager") { // user.jobTitle is now incorrect } 
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There are valid reasons to use assignment operators in conditional statements. However, it can be difficult to tell whether a specific assignment was intentional.

Rule Details

This rule disallows ambiguous assignment operators in test conditions of if, for, while, and do...while statements.

Options

This rule has a string option:

• "except-parens" (default) allows assignments in test conditions only if they are enclosed in parentheses (for example, to allow reassigning a variable in the test of a while or do...while loop).
• "always" disallows all assignments in test conditions.

except-parens

Examples of incorrect code for this rule with the default "except-parens" option:

/*eslint no-cond-assign: "error"*/ // Unintentional assignment let x; if (x = 0) { const b = 1; } // Practical example that is similar to an error const setHeight = function (someNode) { do { someNode.height = "100px"; } while (someNode = someNode.parentNode); } 
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Examples of correct code for this rule with the default "except-parens" option:

/*eslint no-cond-assign: "error"*/ // Assignment replaced by comparison let x; if (x === 0) { const b = 1; } // Practical example that wraps the assignment in parentheses const setHeight = function (someNode) { do { someNode.height = "100px"; } while ((someNode = someNode.parentNode)); } // Practical example that wraps the assignment and tests for 'null' const set_height = function (someNode) { do { someNode.height = "100px"; } while ((someNode = someNode.parentNode) !== null); } 
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always

Examples of incorrect code for this rule with the "always" option:

/*eslint no-cond-assign: ["error", "always"]*/ // Unintentional assignment let x; if (x = 0) { const b = 1; } // Practical example that is similar to an error const setHeight = function (someNode) { do { someNode.height = "100px"; } while (someNode = someNode.parentNode); } // Practical example that wraps the assignment in parentheses const set_height = function (someNode) { do { someNode.height = "100px"; } while ((someNode = someNode.parentNode)); } // Practical example that wraps the assignment and tests for 'null' const heightSetter = function (someNode) { do { someNode.height = "100px"; } while ((someNode = someNode.parentNode) !== null); } 
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Examples of correct code for this rule with the "always" option:

/*eslint no-cond-assign: ["error", "always"]*/ // Assignment replaced by comparison let x; if (x === 0) { const b = 1; } 
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Related Rules

• no-extra-parens

Version

This rule was introduced in ESLint v0.0.9.

Resources

• Rule source
• Tests source