┌─────────────────────────────────────────────────────────────────────────┐
│ WHAT TYPE OF ERROR ARE YOU HANDLING?                                    │
├─────────────────────────────────────────────────────────────────────────┤
│                                                                         │
│ ► Validation error (must prevent save)?                                 │
│   └─► frappe.throw() in validate event                                  │
│                                                                         │
│ ► Warning (inform user, allow continue)?                                │
│   └─► frappe.msgprint() with indicator                                  │
│                                                                         │
│ ► Server call might fail?                                               │
│   └─► try/catch with async/await OR callback error handling             │
│                                                                         │
│ ► Field value invalid (not blocking)?                                   │
│   └─► frm.set_intro() or field description                              │
│                                                                         │
│ ► Need to debug/trace?                                                  │
│   └─► console.log/warn/error + frappe.show_alert for dev                │
│                                                                         │
│ ► Unexpected error in any code?                                         │
│   └─► Wrap in try/catch, log error, show user-friendly message          │
│                                                                         │
└─────────────────────────────────────────────────────────────────────────┘

Error Feedback Methods

Quick Reference

Method	Blocks Save?	User Action	Use For
`frappe.throw()`	✅ YES	Must dismiss	Validation errors
`frappe.msgprint()`	❌ NO	Must dismiss	Important info/warnings
`frappe.show_alert()`	❌ NO	Auto-dismiss	Success/info feedback
`frm.set_intro()`	❌ NO	None	Form-level warnings
`frm.dashboard.set_headline()`	❌ NO	None	Status indicators
`console.error()`	❌ NO	None	Debugging only

frappe.throw() - Blocking Error

// Basic throw - stops execution, prevents save
frappe.throw(__('Customer is required'));

// With title
frappe.throw({
    title: __('Validation Error'),
    message: __('Amount cannot be negative')
});

// With indicator color
frappe.throw({
    message: __('Credit limit exceeded'),
    indicator: 'red'
});

CRITICAL: Only use frappe.throw() in validate event to prevent save. Using it elsewhere stops script execution but doesn't prevent form actions.

frappe.msgprint() - Non-Blocking Alert

// Simple message
frappe.msgprint(__('Document will be processed'));

// With title and indicator
frappe.msgprint({
    title: __('Warning'),
    message: __('Stock is running low'),
    indicator: 'orange'
});

// With primary action button
frappe.msgprint({
    title: __('Confirm Action'),
    message: __('This will archive 50 records. Continue?'),
    primary_action: {
        label: __('Yes, Archive'),
        action: () => {
            // perform action
            frappe.hide_msgprint();
        }
    }
});

frappe.show_alert() - Toast Notification

// Success (green, auto-dismiss)
frappe.show_alert({
    message: __('Saved successfully'),
    indicator: 'green'
}, 3);  // 3 seconds

// Warning (orange)
frappe.show_alert({
    message: __('Some items are out of stock'),
    indicator: 'orange'
}, 5);

// Error (red)
frappe.show_alert({
    message: __('Failed to fetch data'),
    indicator: 'red'
}, 5);

Error Handling Patterns

Pattern 1: Synchronous Validation

frappe.ui.form.on('Sales Order', {
    validate(frm) {
        // Multiple validations - collect errors
        let errors = [];
        
        if (!frm.doc.customer) {
            errors.push(__('Customer is required'));
        }
        
        if (frm.doc.grand_total <= 0) {
            errors.push(__('Total must be greater than zero'));
        }
        
        if (!frm.doc.items || frm.doc.items.length === 0) {
            errors.push(__('At least one item is required'));
        }
        
        // Throw all errors at once
        if (errors.length > 0) {
            frappe.throw({
                title: __('Validation Errors'),
                message: errors.join('<br>')
            });
        }
    }
});

Pattern 2: Async Server Call with Error Handling

frappe.ui.form.on('Sales Order', {
    async customer(frm) {
        if (!frm.doc.customer) return;
        
        try {
            let r = await frappe.call({
                method: 'myapp.api.get_customer_details',
                args: { customer: frm.doc.customer }
            });
            
            if (r.message) {
                frm.set_value('credit_limit', r.message.credit_limit);
            }
        } catch (error) {
            console.error('Failed to fetch customer:', error);
            frappe.show_alert({
                message: __('Could not load customer details'),
                indicator: 'red'
            }, 5);
            // Don't throw - allow user to continue
        }
    }
});

Pattern 3: Async Validation with Server Check

frappe.ui.form.on('Sales Order', {
    async validate(frm) {
        // Server-side validation
        try {
            let r = await frappe.call({
                method: 'myapp.api.validate_order',
                args: { 
                    customer: frm.doc.customer,
                    total: frm.doc.grand_total 
                }
            });
            
            if (r.message && !r.message.valid) {
                frappe.throw({
                    title: __('Validation Failed'),
                    message: r.message.error
                });
            }
        } catch (error) {
            // Server error - decide: block or allow?
            console.error('Validation call failed:', error);
            
            // Option 1: Block save on server error (safer)
            frappe.throw(__('Could not validate. Please try again.'));
            
            // Option 2: Allow save with warning (use with caution)
            // frappe.show_alert({
            //     message: __('Validation skipped due to server error'),
            //     indicator: 'orange'
            // }, 5);
        }
    }
});

Pattern 4: frappe.call Callback Error Handling

// When not using async/await
frappe.call({
    method: 'myapp.api.process_data',
    args: { doc_name: frm.doc.name },
    freeze: true,
    freeze_message: __('Processing...'),
    callback: (r) => {
        if (r.message) {
            frappe.show_alert({
                message: __('Processing complete'),
                indicator: 'green'
            });
            frm.reload_doc();
        }
    },
    error: (r) => {
        // Server returned error (4xx, 5xx)
        console.error('API Error:', r);
        frappe.msgprint({
            title: __('Error'),
            message: __('Processing failed. Please try again.'),
            indicator: 'red'
        });
    }
});

Pattern 5: Child Table Validation

frappe.ui.form.on('Sales Invoice', {
    validate(frm) {
        let errors = [];
        
        (frm.doc.items || []).forEach((row, idx) => {
            if (!row.item_code) {
                errors.push(__('Row {0}: Item is required', [idx + 1]));
            }
            if (row.qty <= 0) {
                errors.push(__('Row {0}: Quantity must be positive', [idx + 1]));
            }
            if (row.rate < 0) {
                errors.push(__('Row {0}: Rate cannot be negative', [idx + 1]));
            }
        });
        
        if (errors.length > 0) {
            frappe.throw({
                title: __('Item Errors'),
                message: errors.join('<br>')
            });
        }
    }
});

Pattern 6: Graceful Degradation

frappe.ui.form.on('Sales Order', {
    async refresh(frm) {
        // Try to load extra data, but don't fail if unavailable
        try {
            let stock = await frappe.call({
                method: 'myapp.api.get_stock_summary',
                args: { items: frm.doc.items.map(r => r.item_code) }
            });
            
            if (stock.message) {
                render_stock_dashboard(frm, stock.message);
            }
        } catch (error) {
            // Log but don't disturb user
            console.warn('Stock dashboard unavailable:', error);
            // Optionally show subtle indicator
            frm.dashboard.set_headline(
                __('Stock info unavailable'),
                'orange'
            );
        }
    }
});

See: references/patterns.md for more error handling patterns.

Debugging Techniques

Console Logging

// Development debugging
frappe.ui.form.on('Sales Order', {
    customer(frm) {
        console.log('Customer changed:', frm.doc.customer);
        console.log('Full doc:', JSON.parse(JSON.stringify(frm.doc)));
        
        // Trace child table
        console.table(frm.doc.items);
    }
});

Conditional Debugging

// Only log in development
const DEBUG = frappe.boot.developer_mode;

function debugLog(...args) {
    if (DEBUG) {
        console.log('[MyApp]', ...args);
    }
}

frappe.ui.form.on('Sales Order', {
    validate(frm) {
        debugLog('Validating:', frm.doc.name);
        // validation logic
    }
});

Error Stack Traces

try {
    riskyOperation();
} catch (error) {
    console.error('Error details:', {
        message: error.message,
        stack: error.stack,
        doc: frm.doc.name
    });
    
    // User-friendly message (no technical details)
    frappe.msgprint({
        title: __('Error'),
        message: __('An unexpected error occurred. Please contact support.'),
        indicator: 'red'
    });
}

Critical Rules

✅ ALWAYS

Wrap async calls in try/catch - Uncaught Promise rejections crash silently
Use __() for error messages - All user-facing text must be translatable
Log errors to console - Helps debugging without exposing to users
Collect multiple validation errors - Don't throw on first error
Provide actionable error messages - Tell user how to fix it

❌ NEVER

Don't expose technical errors to users - Catch and translate
Don't use frappe.throw() outside validate - It stops execution but doesn't prevent save
Don't ignore server call failures - Always handle error callback
Don't use alert() or confirm() - Use frappe methods instead
Don't leave console.log in production - Use conditional debugging

Quick Reference: Error Message Quality

// ❌ BAD - Technical, not actionable
frappe.throw('NullPointerException in line 42');
frappe.throw('Query failed');
frappe.throw('Error');

// ✅ GOOD - Clear, actionable
frappe.throw(__('Please select a customer before adding items'));
frappe.throw(__('Amount {0} exceeds credit limit of {1}', [amount, limit]));
frappe.throw(__('Could not save. Please check your internet connection and try again.'));

Reference Files

File	Contents
`references/patterns.md`	Complete error handling patterns
`references/examples.md`	Full working examples
`references/anti-patterns.md`	Common mistakes to avoid

Error Feedback Methods

Quick Reference

frappe.throw() - Blocking Error

frappe.msgprint() - Non-Blocking Alert

frappe.show_alert() - Toast Notification

Error Handling Patterns

Pattern 1: Synchronous Validation

Pattern 2: Async Server Call with Error Handling

Pattern 3: Async Validation with Server Check

Pattern 4: frappe.call Callback Error Handling

Pattern 5: Child Table Validation

Pattern 6: Graceful Degradation

Debugging Techniques

Console Logging

Conditional Debugging

Error Stack Traces

Critical Rules

✅ ALWAYS

❌ NEVER

Quick Reference: Error Message Quality

Reference Files

See Also

erpnext-errors-clientscripts

ERPNext Client Scripts - Error Handling

Main Decision: How to Handle the Error?