tv4: add const support

jsonform/tv4.js

@@ -725,6 +725,9 @@ ValidatorContext.prototype.validateBasic = function validateBasic(data, schema,
 	if (error = this.validateType(data, schema, dataPointerPath)) {
 		return error.prefixWith(null, "type");
 	}
+	if (error = this.validateConst(data, schema, dataPointerPath)) {
+		return error.prefixWith(null, "const");
+	}
 	if (error = this.validateEnum(data, schema, dataPointerPath)) {
 		return error.prefixWith(null, "type");
 	}
@@ -755,6 +758,14 @@ ValidatorContext.prototype.validateType = function validateType(data, schema) {
 	return this.createError(ErrorCodes.INVALID_TYPE, {type: dataType, expected: allowedTypes.join("/")}, '', '', null, data, schema);
 };
 
+ValidatorContext.prototype.validateConst = function validateConst(data, schema) {
+	if (schema.const === undefined ||
+			recursiveCompare(data, schema.const)) {
+		return null;
+	}
+	return this.createError(ErrorCodes.CONST_NOT_EQUAL, {}, '', '', null, data, schema);
+};
+
 ValidatorContext.prototype.validateEnum = function validateEnum(data, schema) {
 	if (schema["enum"] === undefined) {
 		return null;
@@ -1379,6 +1390,7 @@ var ErrorCodes = {
 	ONE_OF_MULTIPLE: 12,
 	NOT_PASSED: 13,
 	BOOLEAN_SCHEMA_FALSE: 14,
+	CONST_NOT_EQUAL: 15,
 	// Numeric errors
 	NUMBER_MULTIPLE_OF: 100,
 	NUMBER_MINIMUM: 101,
@@ -1421,6 +1433,7 @@ var ErrorMessagesDefault = {
 	ONE_OF_MULTIPLE: "Data is valid against more than one schema from \"oneOf\": indices {index1} and {index2}",
 	NOT_PASSED: "Data matches schema from \"not\"",
 	BOOLEAN_SCHEMA_FALSE: "Schema does not allow any data",
+	CONST_NOT_EQUAL: "Data does not match schema.const",
 	// Numeric errors
 	NUMBER_MULTIPLE_OF: "Value {value} is not a multiple of {multipleOf}",
 	NUMBER_MINIMUM: "Value {value} is less than minimum {minimum}",