How to fix the 'push is not a function' error
November 4, 2023
push method on a variable that is not an array. This guide aims to help engineers diagnose and solve this error efficiently.
Recognize the error
push method is strictly an array method. The error is thrown when the method is called on something that is not an array - this could be due to the variable being of a different type or uninitialized.
Check the variable type
First, confirm that the variable you're attempting to
push onto is indeed an array.
Ensure proper initialization
Variables must be initialized as arrays before using the
Incorrect initializations to look out for:
Review the variable assignment
A variable may have been reassigned to a non-array type. Trace back to see if the variable has been changed and ensure it remains an array throughout its lifecycle.
Watch for method chaining
When chaining methods, ensure that each method returns an array if you plan to call
Look for shadowing issues
Variable shadowing occurs when a variable in a local scope uses the same name as a variable in the outer scope.
Consider the environment
Array.prototype.push. For example, ECMAScript 3 does not support it in strict mode.
Handle TypeScript type assertions
If using TypeScript, ensure that your type assertions are correct.
Instead, assert the variable as an array:
Inspect third-party code
If using external libraries, check their documentation to ensure that the methods you are using return arrays when expected.
console.log or breakpoints to inspect the type of your variable before the
Write unit tests to verify the type and integrity of the variables throughout their lifecycle.
Avoid mutating state
Consider using immutable data patterns to prevent accidental reassignment or mutation that could lead to type-related errors.
Use TypeScript or Flow
Leverage TypeScript or Flow for static type checking to catch these errors during the development process rather than at runtime.
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