/**
* @license
* Copyright The Closure Library Authors.
* SPDX-License-Identifier: Apache-2.0
*/
/**
* @fileoverview Utilities for creating functions. Loosely inspired by these
* java classes from the Guava library:
* com.google.common.base.Functions
* https://google.github.io/guava/releases/snapshot-jre/api/docs/index.html?com/google/common/base/Functions.html
*
* com.google.common.base.Predicates
* https://google.github.io/guava/releases/snapshot-jre/api/docs/index.html?com/google/common/base/Predicates.html
*
* More about these can be found at
* https://github.com/google/guava/wiki/FunctionalExplained
*/
goog.provide('goog.functions');
/**
* Creates a function that always returns the same value.
* @param {T} retValue The value to return.
* @return {function():T} The new function.
* @template T
*/
goog.functions.constant = function(retValue) {
'use strict';
return function() {
'use strict';
return retValue;
};
};
/**
* Always returns false.
* @type {function(...): boolean}
*/
goog.functions.FALSE = function() {
'use strict';
return false;
};
/**
* Always returns true.
* @type {function(...): boolean}
*/
goog.functions.TRUE = function() {
'use strict';
return true;
};
/**
* Always returns `null`.
* @type {function(...): null}
*/
goog.functions.NULL = function() {
'use strict';
return null;
};
/**
* Always returns `undefined`.
* @type {function(...): undefined}
*/
goog.functions.UNDEFINED = function() {
return undefined;
};
/**
* Always returns `undefined` (loosely-typed version).
* @type {!Function}
*/
goog.functions.EMPTY = /** @type {?} */ (goog.functions.UNDEFINED);
/**
* A simple function that returns the first argument of whatever is passed
* into it.
* @param {T=} opt_returnValue The single value that will be returned.
* @param {...*} var_args Optional trailing arguments. These are ignored.
* @return {T} The first argument passed in, or undefined if nothing was passed.
* @template T
*/
goog.functions.identity = function(opt_returnValue, var_args) {
'use strict';
return opt_returnValue;
};
/**
* Creates a function that always throws an error with the given message.
* @param {string} message The error message.
* @return {!Function} The error-throwing function.
*/
goog.functions.error = function(message) {
'use strict';
return function() {
'use strict';
throw new Error(message);
};
};
/**
* Creates a function that throws the given object.
* @param {*} err An object to be thrown.
* @return {!Function} The error-throwing function.
*/
goog.functions.fail = function(err) {
'use strict';
return function() {
'use strict';
throw err;
};
};
/**
* Given a function, create a function that keeps opt_numArgs arguments and
* silently discards all additional arguments.
* @param {Function} f The original function.
* @param {number=} opt_numArgs The number of arguments to keep. Defaults to 0.
* @return {!Function} A version of f that only keeps the first opt_numArgs
* arguments.
*/
goog.functions.lock = function(f, opt_numArgs) {
'use strict';
opt_numArgs = opt_numArgs || 0;
return function() {
'use strict';
const self = /** @type {*} */ (this);
return f.apply(self, Array.prototype.slice.call(arguments, 0, opt_numArgs));
};
};
/**
* Creates a function that returns its nth argument.
* @param {number} n The position of the return argument.
* @return {!Function} A new function.
*/
goog.functions.nth = function(n) {
'use strict';
return function() {
'use strict';
return arguments[n];
};
};
/**
* Like goog.partial(), except that arguments are added after arguments to the
* returned function.
*
* Usage:
* function f(arg1, arg2, arg3, arg4) { ... }
* var g = goog.functions.partialRight(f, arg3, arg4);
* g(arg1, arg2);
*
* @param {!Function} fn A function to partially apply.
* @param {...*} var_args Additional arguments that are partially applied to fn
* at the end.
* @return {!Function} A partially-applied form of the function goog.partial()
* was invoked as a method of.
*/
goog.functions.partialRight = function(fn, var_args) {
'use strict';
const rightArgs = Array.prototype.slice.call(arguments, 1);
return function() {
'use strict';
// Even in strict mode, IE10/11 and Edge (non-Chromium) use global context
// when free-calling functions. To catch cases where people were using this
// erroneously, we explicitly change the context to undefined to match
// strict mode specifications.
let self = /** @type {*} */ (this);
if (self === goog.global) {
self = undefined;
}
const newArgs = Array.prototype.slice.call(arguments);
newArgs.push.apply(newArgs, rightArgs);
return fn.apply(self, newArgs);
};
};
/**
* Given a function, create a new function that swallows its return value
* and replaces it with a new one.
* @param {Function} f A function.
* @param {T} retValue A new return value.
* @return {function(...?):T} A new function.
* @template T
*/
goog.functions.withReturnValue = function(f, retValue) {
'use strict';
return goog.functions.sequence(f, goog.functions.constant(retValue));
};
/**
* Creates a function that returns whether its argument equals the given value.
*
* Example:
* var key = goog.object.findKey(obj, goog.functions.equalTo('needle'));
*
* @param {*} value The value to compare to.
* @param {boolean=} opt_useLooseComparison Whether to use a loose (==)
* comparison rather than a strict (===) one. Defaults to false.
* @return {function(*):boolean} The new function.
*/
goog.functions.equalTo = function(value, opt_useLooseComparison) {
'use strict';
return function(other) {
'use strict';
return opt_useLooseComparison ? (value == other) : (value === other);
};
};
/**
* Creates the composition of the functions passed in.
* For example, (goog.functions.compose(f, g))(a) is equivalent to f(g(a)).
* @param {function(...?):T} fn The final function.
* @param {...Function} var_args A list of functions.
* @return {function(...?):T} The composition of all inputs.
* @template T
*/
goog.functions.compose = function(fn, var_args) {
'use strict';
const functions = arguments;
const length = functions.length;
return function() {
'use strict';
const self = /** @type {*} */ (this);
let result;
if (length) {
result = functions[length - 1].apply(self, arguments);
}
for (let i = length - 2; i >= 0; i--) {
result = functions[i].call(self, result);
}
return result;
};
};
/**
* Creates a function that calls the functions passed in in sequence, and
* returns the value of the last function. For example,
* (goog.functions.sequence(f, g))(x) is equivalent to f(x),g(x).
* @param {...Function} var_args A list of functions.
* @return {!Function} A function that calls all inputs in sequence.
*/
goog.functions.sequence = function(var_args) {
'use strict';
const functions = arguments;
const length = functions.length;
return function() {
'use strict';
const self = /** @type {*} */ (this);
let result;
for (let i = 0; i < length; i++) {
result = functions[i].apply(self, arguments);
}
return result;
};
};
/**
* Creates a function that returns true if each of its components evaluates
* to true. The components are evaluated in order, and the evaluation will be
* short-circuited as soon as a function returns false.
* For example, (goog.functions.and(f, g))(x) is equivalent to f(x) && g(x).
* @param {...Function} var_args A list of functions.
* @return {function(...?):boolean} A function that ANDs its component
* functions.
*/
goog.functions.and = function(var_args) {
'use strict';
const functions = arguments;
const length = functions.length;
return function() {
'use strict';
const self = /** @type {*} */ (this);
for (let i = 0; i < length; i++) {
if (!functions[i].apply(self, arguments)) {
return false;
}
}
return true;
};
};
/**
* Creates a function that returns true if any of its components evaluates
* to true. The components are evaluated in order, and the evaluation will be
* short-circuited as soon as a function returns true.
* For example, (goog.functions.or(f, g))(x) is equivalent to f(x) || g(x).
* @param {...Function} var_args A list of functions.
* @return {function(...?):boolean} A function that ORs its component
* functions.
*/
goog.functions.or = function(var_args) {
'use strict';
const functions = arguments;
const length = functions.length;
return function() {
'use strict';
const self = /** @type {*} */ (this);
for (let i = 0; i < length; i++) {
if (functions[i].apply(self, arguments)) {
return true;
}
}
return false;
};
};
/**
* Creates a function that returns the Boolean opposite of a provided function.
* For example, (goog.functions.not(f))(x) is equivalent to !f(x).
* @param {!Function} f The original function.
* @return {function(...?):boolean} A function that delegates to f and returns
* opposite.
*/
goog.functions.not = function(f) {
'use strict';
return function() {
'use strict';
const self = /** @type {*} */ (this);
return !f.apply(self, arguments);
};
};
/**
* Generic factory function to construct an object given the constructor
* and the arguments. Intended to be bound to create object factories.
*
* Example:
*
* var factory = goog.partial(goog.functions.create, Class);
*
* @param {function(new:T, ...)} constructor The constructor for the Object.
* @param {...*} var_args The arguments to be passed to the constructor.
* @return {T} A new instance of the class given in `constructor`.
* @template T
* @deprecated This function does not work with ES6 class constructors. Use
* arrow functions + spread args instead.
*/
goog.functions.create = function(constructor, var_args) {
'use strict';
/**
* @constructor
* @final
*/
const temp = function() {};
temp.prototype = constructor.prototype;
// obj will have constructor's prototype in its chain and
// 'obj instanceof constructor' will be true.
const obj = new temp();
// obj is initialized by constructor.
// arguments is only array-like so lacks shift(), but can be used with
// the Array prototype function.
constructor.apply(obj, Array.prototype.slice.call(arguments, 1));
return obj;
};
/**
* @define {boolean} Whether the return value cache should be used.
* This should only be used to disable caches when testing.
*/
goog.functions.CACHE_RETURN_VALUE =
goog.define('goog.functions.CACHE_RETURN_VALUE', true);
/**
* Gives a wrapper function that caches the return value of a parameterless
* function when first called.
*
* When called for the first time, the given function is called and its
* return value is cached (thus this is only appropriate for idempotent
* functions). Subsequent calls will return the cached return value. This
* allows the evaluation of expensive functions to be delayed until first used.
*
* To cache the return values of functions with parameters, see goog.memoize.
*
* @param {function():T} fn A function to lazily evaluate.
* @return {function():T} A wrapped version the function.
* @template T
*/
goog.functions.cacheReturnValue = function(fn) {
'use strict';
let called = false;
let value;
return function() {
'use strict';
if (!goog.functions.CACHE_RETURN_VALUE) {
return fn();
}
if (!called) {
value = fn();
called = true;
}
return value;
};
};
/**
* Wraps a function to allow it to be called, at most, once. All
* additional calls are no-ops.
*
* This is particularly useful for initialization functions
* that should be called, at most, once.
*
* @param {function():*} f Function to call.
* @return {function():undefined} Wrapped function.
*/
goog.functions.once = function(f) {
'use strict';
// Keep a reference to the function that we null out when we're done with
// it -- that way, the function can be GC'd when we're done with it.
let inner = f;
return function() {
'use strict';
if (inner) {
const tmp = inner;
inner = null;
tmp();
}
};
};
/**
* Wraps a function to allow it to be called, at most, once per interval
* (specified in milliseconds). If the wrapper function is called N times within
* that interval, only the Nth call will go through.
*
* This is particularly useful for batching up repeated actions where the
* last action should win. This can be used, for example, for refreshing an
* autocomplete pop-up every so often rather than updating with every keystroke,
* since the final text typed by the user is the one that should produce the
* final autocomplete results. For more stateful debouncing with support for
* pausing, resuming, and canceling debounced actions, use
* `goog.async.Debouncer`.
*
* @param {function(this:SCOPE, ...?)} f Function to call.
* @param {number} interval Interval over which to debounce. The function will
* only be called after the full interval has elapsed since the last call.
* @param {SCOPE=} opt_scope Object in whose scope to call the function.
* @return {function(...?): undefined} Wrapped function.
* @template SCOPE
*/
goog.functions.debounce = function(f, interval, opt_scope) {
'use strict';
let timeout = 0;
return /** @type {function(...?)} */ (function(var_args) {
'use strict';
goog.global.clearTimeout(timeout);
const args = arguments;
timeout = goog.global.setTimeout(function() {
'use strict';
f.apply(opt_scope, args);
}, interval);
});
};
/**
* Wraps a function to allow it to be called, at most, once per interval
* (specified in milliseconds). If the wrapper function is called N times in
* that interval, both the 1st and the Nth calls will go through.
*
* This is particularly useful for limiting repeated user requests where the
* the last action should win, but you also don't want to wait until the end of
* the interval before sending a request out, as it leads to a perception of
* slowness for the user.
*
* @param {function(this:SCOPE, ...?)} f Function to call.
* @param {number} interval Interval over which to throttle. The function can
* only be called once per interval.
* @param {SCOPE=} opt_scope Object in whose scope to call the function.
* @return {function(...?): undefined} Wrapped function.
* @template SCOPE
*/
goog.functions.throttle = function(f, interval, opt_scope) {
'use strict';
let timeout = 0;
let shouldFire = false;
let storedArgs = [];
const handleTimeout = function() {
'use strict';
timeout = 0;
if (shouldFire) {
shouldFire = false;
fire();
}
};
const fire = function() {
'use strict';
timeout = goog.global.setTimeout(handleTimeout, interval);
let args = storedArgs;
storedArgs = []; // Avoid a space leak by clearing stored arguments.
f.apply(opt_scope, args);
};
return /** @type {function(...?)} */ (function(var_args) {
'use strict';
storedArgs = arguments;
if (!timeout) {
fire();
} else {
shouldFire = true;
}
});
};
/**
* Wraps a function to allow it to be called, at most, once per interval
* (specified in milliseconds). If the wrapper function is called N times within
* that interval, only the 1st call will go through.
*
* This is particularly useful for limiting repeated user requests where the
* first request is guaranteed to have all the data required to perform the
* final action, so there's no need to wait until the end of the interval before
* sending the request out.
*
* @param {function(this:SCOPE, ...?)} f Function to call.
* @param {number} interval Interval over which to rate-limit. The function will
* only be called once per interval, and ignored for the remainer of the
* interval.
* @param {SCOPE=} opt_scope Object in whose scope to call the function.
* @return {function(...?): undefined} Wrapped function.
* @template SCOPE
*/
goog.functions.rateLimit = function(f, interval, opt_scope) {
'use strict';
let timeout = 0;
const handleTimeout = function() {
'use strict';
timeout = 0;
};
return /** @type {function(...?)} */ (function(var_args) {
'use strict';
if (!timeout) {
timeout = goog.global.setTimeout(handleTimeout, interval);
f.apply(opt_scope, arguments);
}
});
};
/**
* Returns true if the specified value is a function.
* @param {*} val Variable to test.
* @return {boolean} Whether variable is a function.
*/
goog.functions.isFunction = (val) => {
return typeof val === 'function';
};
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