What is Node.js util.deprecate() ?
In Node.js, util.deprecate() wraps around a function in such a way that the function is marked deprecated. util.deprecate() throws a warning on STDERR, along with the supplied ERRCODE.
util.deprecate() is included in the util module. The util module can be accessed as follows:
const util = require('util');
Prototype
const funcName = util.deprecate(fn,msg,code)
Parameters
-
fn: The deprecated function -
msg: The string that will be displayed onSTDERR -
code(optional): The deprecated code. See the full list of deprecated codes here.
Return value
util.deprecate() wraps and returns the function that is passed as the argument in such a way that it emits a warning onto the STDERR.
When util.deprecate() is called, it emits a DeprecationWarning using the ‘warning’ event. If the same code is provided for multiple calls, the warning will only be printed once.
Code
const util = require('util')const test = util.deprecate(() => {console.log("DEPRICATED FUNC CALLED")},"test() is deprecated. Use updatedTest() instead",'ERR001')test()
Here, we wrap the test() function using the util.deprecate() method. When test() is called, it emits a warning that is printed on STDERR and the deprecated code is executed.
If either the --no-deprecation or --no-warnings command-line flags are utilized, or if the process.noDeprecation property is set to true before the first deprecation warning, the util.deprecate() method does nothing.
If the --trace-deprecation or --trace-warnings command-line flags are set, or the process.traceDeprecation property is set to true, a warning and a stack trace are printed to STDERR when we invoke the deprecated function for the first time.
If the --throw-deprecation command-line flag is set, or the process.throwDeprecation property is set to true, then, at that point, an exception will be thrown when the deprecated function is called.
The --throw-deprecation command-line flag and process.throwDeprecation property outweigh --trace-deprecation and process.traceDeprecation.
