angular/angular · error · RuntimeError

EXPRESSION_CHANGED_AFTER_CHECKED

EXPRESSION_CHANGED_AFTER_CHECKED

Error message

ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked. Previous value for '${propName}': '${formatValue(oldValue)}'. Current value: '${formatValue(currValue)}'.

What it means

Error "ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked. Previous value for '${propName}': '${formatValue(oldValue)}'. Current value: '${formatValue(currValue)}'." thrown in angular/angular.

Source

Thrown at packages/core/src/render3/errors.ts:85

  oldValue: any,
  currValue: any,
  propName: string | undefined,
  lView: LView,
): never {
  const hostComponentDef = getDeclarationComponentDef(lView);
  const componentClassName = hostComponentDef?.type?.name;
  const field = propName ? ` for '${propName}'` : '';
  let msg = `ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked. Previous value${field}: '${formatValue(
    oldValue,
  )}'. Current value: '${formatValue(currValue)}'.${
    componentClassName ? ` Expression location: ${componentClassName} component` : ''
  }`;
  if (creationMode) {
    msg +=
      ` It seems like the view has been created after its parent and its children have been dirty checked.` +
      ` Has it been created in a change detection hook?`;
  }
  throw new RuntimeError(RuntimeErrorCode.EXPRESSION_CHANGED_AFTER_CHECKED, msg);
}

function formatValue(value: unknown): string {
  let strValue: string = String(value);

  // JSON.stringify will throw on circular references
  try {
    if (Array.isArray(value) || strValue === '[object Object]') {
      strValue = JSON.stringify(value);
    }
  } catch (error) {}
  return strValue.length > VALUE_STRING_LENGTH_LIMIT
    ? strValue.substring(0, VALUE_STRING_LENGTH_LIMIT) + '…'
    : strValue;
}

function constructDetailsForInterpolation(
  lView: LView,

View on GitHub (pinned to 51cb07e980)

Solutions

1. Update the bound value before change detection (e.g. in ngOnInit) or defer the update with setTimeout/signals.

When it happens

Trigger: Thrown at packages/core/src/render3/errors.ts:85 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of angular/angular@51cb07e980 (2026-08-22). Data as JSON: /api/errors/bc1ae855273fc45e. Report an issue: GitHub.