ifError() : Error Handling Expression

Summary

Evaluate an expression and return a fallback value if an error occurs. This provides graceful error handling within binding expressions.

Signature

ifError(expression, fallbackValue)

Parameters

Returns

Type: Any (matches type of expression or fallbackValue)

Returns the result of expression if successful, otherwise returns fallbackValue if an error occurs.

Examples

Safe Division

<p>Average: </p>

Data:

doc.Params["model"] = new {
    total = 100,
    count = 0  // Would cause division by zero
};

Output:

<p>Average: 0</p>

Safe Property Access

  <p>: </p>

Data:

doc.Params["model"] = new {
    items = new[] {
        new { name = "Item A", details = new { description = "Description A" } },
        new { name = "Item B", details = (object)null }  // Null details
    }
};

Output:

<p>Item A: Description A</p>
<p>Item B: No description available</p>

Safe Type Conversion

<p>Value: </p>

Data:

doc.Params["model"] = new {
    userInput = "not a number"
};

Output:

<p>Value: -1</p>

Safe Date Parsing

  <p>: </p>

Data:

doc.Params["model"] = new {
    records = new[] {
        new { id = "A", dateString = "2024-03-15" },
        new { id = "B", dateString = "not-a-date" }
    }
};

Output:

<p>A: 2024-03-15</p>
<p>B: Invalid date</p>

Safe Array Access

<p>First item: </p>

Data:

doc.Params["model"] = new {
    items = new string[] { }  // Empty array
};

Output:

<p>First item: No items</p>

Notes

• Catches all errors from the expression evaluation
• Does not log or expose error details (use for graceful degradation)
• Both parameters are evaluated, but expression errors are caught
• Useful for:
  • Division by zero protection
  • Null reference handling
  • Type conversion safety
  • Missing property graceful handling
  • Array bounds protection
• Consider using null coalescing operator (??) for simple null checks
• For debugging errors, use `` helper instead
• Performance: Has slight overhead due to error catching
• Best practice: Use when you expect potential errors in data
• Alternative to extensive null checking with ``

See Also

• if Function
• Null Coalesce Operator
• log Helper
• typeof Function