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450What Makes a Component 'Controlled'
451The value Prop on Inputs
452The onChange Handler
453The Basic Pattern: useState + value + onChange
454Accessing Input Values: event.target.value
455Controlled Text Inputs
456Controlled Textareas
457Controlled Select Dropdowns
458Controlled Checkboxes
459Controlled Radio Buttons
460Multi-Select Dropdowns
461The Cursor Jump Problem
462Why Controlled Components Re-render on Every Change
463What 'Single Source of Truth' Means
464The Two-State Problem in Uncontrolled Inputs
465Controlled: State Drives the DOM
466Why onChange is Required with value
467The setState → Re-render → DOM Update Flow
468Benefits: Validation and Formatting On-the-Fly
469Benefits: Conditional Rendering Based on Input
470Benefits: Resetting Inputs Programmatically
471Tradeoff: Extra Re-renders
472Every Keystroke Triggers a Re-render
473Measuring the Actual Performance Impact
474When Re-render Cost Becomes a Problem
475The Parent Component Re-render Chain
476Mitigating Cost: Lift State Down
477Mitigating Cost: Debouncing State Updates
478When Uncontrolled is the Better Choice
479Modern Solutions: React Hook Form's Performance
480The Standard Controlled Input Pattern
481Text Input: value and onChange
482Textarea: Same Pattern, Different Element
483Checkbox: checked and onChange
484Radio Buttons: Grouping by name
485Select Dropdown: value on the select Element
486Multi-Select: value as Array
487Number Input: Parsing and Validation
488Generic onChange Handler Pattern
489Controlled Input Recipe Reference

450What Makes a Component 'Controlled'
451The value Prop on Inputs
452The onChange Handler
453The Basic Pattern: useState + value + onChange
454Accessing Input Values: event.target.value
455Controlled Text Inputs
456Controlled Textareas
457Controlled Select Dropdowns
458Controlled Checkboxes
459Controlled Radio Buttons
460Multi-Select Dropdowns
461The Cursor Jump Problem
462Why Controlled Components Re-render on Every Change
463What 'Single Source of Truth' Means
464The Two-State Problem in Uncontrolled Inputs
465Controlled: State Drives the DOM
466Why onChange is Required with value
467The setState → Re-render → DOM Update Flow
468Benefits: Validation and Formatting On-the-Fly
469Benefits: Conditional Rendering Based on Input
470Benefits: Resetting Inputs Programmatically
471Tradeoff: Extra Re-renders
472Every Keystroke Triggers a Re-render
473Measuring the Actual Performance Impact
474When Re-render Cost Becomes a Problem
475The Parent Component Re-render Chain
476Mitigating Cost: Lift State Down
477Mitigating Cost: Debouncing State Updates
478When Uncontrolled is the Better Choice
479Modern Solutions: React Hook Form's Performance
480The Standard Controlled Input Pattern
481Text Input: value and onChange
482Textarea: Same Pattern, Different Element
483Checkbox: checked and onChange
484Radio Buttons: Grouping by name
485Select Dropdown: value on the select Element
486Multi-Select: value as Array
487Number Input: Parsing and Validation
488Generic onChange Handler Pattern
489Controlled Input Recipe Reference

Lesson 487 of 2,396·13. Controlled ComponentsPro lesson

Number Input: Parsing and Validation

Parse e.target.value with Number() or parseInt() and handle empty strings appropriately.

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