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# Library goog.asserts

Function Summary
| `assert(<Any Type> condition, string= opt_message, <Any Type> var_args) ⇒ <Any Type>` Checks if the condition evaluates to true if goog.asserts.ENABLE_ASSERTS is true.
| `assertArray(<Any Type> value, string= opt_message, <Any Type> var_args) ⇒ !Array` Checks if the value is an Array if goog.asserts.ENABLE_ASSERTS is true.
| `assertBoolean(<Any Type> value, string= opt_message, <Any Type> var_args) ⇒ boolean` Checks if the value is a boolean if goog.asserts.ENABLE_ASSERTS is true.
| `assertFunction(<Any Type> value, string= opt_message, <Any Type> var_args) ⇒ !Function` Checks if the value is a function if goog.asserts.ENABLE_ASSERTS is true.
| `assertInstanceof(<Any Type> value, !Function type, string= opt_message, <Any Type> var_args)` Checks if the value is an instance of the user-defined type if goog.asserts.ENABLE_ASSERTS is true.
| `assertNumber(<Any Type> value, string= opt_message, <Any Type> var_args) ⇒ number` Checks if the value is a number if goog.asserts.ENABLE_ASSERTS is true.
| `assertObject(<Any Type> value, string= opt_message, <Any Type> var_args) ⇒ !Object` Checks if the value is an Object if goog.asserts.ENABLE_ASSERTS is true.
| `assertString(<Any Type> value, string= opt_message, <Any Type> var_args) ⇒ string` Checks if the value is a string if goog.asserts.ENABLE_ASSERTS is true.
| `doAssertFailure_(string defaultMessage, ?Array.<*> defaultArgs, (string|undefined) givenMessage, ?Array.<*> givenArgs)` Throws an exception with the given message and "Assertion failed" prefixed onto it.

`fail(string= opt_message, <Any Type> var_args)`

Fails if goog.asserts.ENABLE_ASSERTS is true. This function is useful in case when we want to add a check in the unreachable area like switch-case statement:

    switch(type) {
    case FOO: doSomething(); break;
    case BAR: doSomethingElse(); break;
    default: goog.assert.fail('Unrecognized type: ' + type);
    // We have only 2 types - "default:" section is unreachable code.
    }