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Summary of the new numerical methods in ES6 (must read)
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- 2018-08-17 14:18:301890browse
This article brings you a summary of the new digital methods in ES6 (a must-read). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.
This article introduces the new numerical methods in ES6 (ECMAScript 6).
This article will introduce you to the new methods and constants of adding Number data type. Of course, the methods employed here are not entirely new, but they can already be moved directly within and/or (e.g. isNaN()). We will practice this with some examples.
Number.isInteger()
The first method I want to introduce is Number.isInteger(). It's new to JavaScript, and you may have defined and used this method before. It determines whether the value passed to the function is an integer. If the function value is true, this method returns, if false, it exits. The implementation of this method is very simple and is native JavaScript syntax. One of the ways to rewrite this function is:
Number.isInteger = Number.isInteger || function (number) {
return typeof number === 'number' && number % 1 === 0;
};
Just for fun, I rewrote this function to use a completely different method:
Number.isInteger = Number.isInteger || function (number) {
return typeof number === 'number' && Math.floor(number) === number;
};
Although both of the above methods can determine Whether the passed parameters are integers, but they do not comply with the ECMAScript 6 specification. So, if you want to rewrite strictly according to ES6 specifications, please start with the following syntax:
Number.isInteger(number)
The parameter number represents the value to be tested.
An example of using this method is shown below:
// prints 'true' console.log(Number.isInteger(19)); // prints 'false' console.log(Number.isInteger(3.5)); // prints 'false' console.log(Number.isInteger([1, 2, 3]));
This method is supported by Node.js and all modern browsers, except Internet Explorer. If you need to support older browsers, you can use a polyfill, such as the one available on the Mozilla Developer Network for Firefox. Take a look at the code below:
if (!Number.isInteger) {
Number.isInteger = function isInteger (nVal) {
return typeof nVal === 'number' &&
isFinite(nVal) &&
nVal > -9007199254740992 &&
nVal < 9007199254740992 &&
Math.floor(nVal) === nVal;
};
}
Number.isNaN()
If you have written JavaScript code before, this method will not be unfamiliar to you. JavaScript has a method called isNaN() exposed through the window object. This method is used to determine whether the test value is equal to NaN. It returns true, otherwise it returns false. However, there is a problem with calling window.isNaN() directly. When the test value is forced to be converted to a number, this method will return a true value. To give you a concrete idea of the problem, all of the following statements will return: true
// prints 'true'
console.log(window.isNaN(0/0));
// prints 'true'
console.log(window.isNaN('test'));
// prints 'true'
console.log(window.isNaN(undefined));
// prints 'true'
console.log(window.isNaN({prop: 'value'}));
What you probably want is a method that only returns true when the passed value is NaN. This is why ECMAScript 6 introduced Number.isNaN(). Its syntax is as follows:
Number.isNaN(value)
这value是您要测试的值。此方法的一些示例用法如下所示：
// prints 'true'
console.log(Number.isNaN(0/0));
// prints 'true'
console.log(Number.isNaN(NaN));
// prints 'false'
console.log(Number.isNaN(undefined));
// prints 'false'
console.log(Number.isNaN({prop: 'value'}));
As you can see, testing the same values we get different results.
This method is supported by Node and all modern browsers, except Internet Explorer. If you want to support other browsers, a very simple polyfill for this method is as follows:
Number.isNaN = Number.isNaN || function (value) {
return value !== value;
};
NaN is the only non-self value in JavaScript, meaning it is the only value that is not equal to itself.
Number.isFinite()
This method has the same background as the previous method. In JavaScript, there is such a method window.isFinite(), which is used to test whether the passed value is a finite number. Unfortunately, it also returns a true value that is coerced to a number, an example like this:
// prints 'true' console.log(window.isFinite(10)); // prints 'true' console.log(window.isFinite(Number.MAX_VALUE)); // prints 'true' console.log(window.isFinite(null)); // prints 'true' console.log(window.isFinite([]));
For this reason, in ECMAScript 6 there is a method called isFinite(). The syntax is as follows:
Number.isFinite(value)
value is the value you want to test. If you test the same value from the previous snippet, you can see the results are different:
// prints 'true' console.log(Number.isFinite(10)); // prints 'true' console.log(Number.isFinite(Number.MAX_VALUE)); // prints 'false' console.log(Number.isFinite(null)); // prints 'false' console.log(Number.isFinite([]));
This method is supported by Node and all modern browsers, except Internet Explorer. You can find its polyfill on the methods page on MDN.
Number.isSafeInteger()
Number.isSafeInteger() is a brand new addition to ES6. It tests whether the passed value is a safe integer, in which case it returns true. A safe integer is defined as an integer that satisfies the following two conditions:
The number can be represented exactly as an IEEE-754 double
number The IEEE-754 representation cannot be the result of rounding any other integer to fit the IEEE-754 representation.
According to this definition, a safe integer is from -(2 to the power of 53-1)contained to 2 to the power of 53-1All integers contained.
Number.isSafeInteger(value)
这value是您要测试的值。此方法的一些示例用法如下所示：
// prints 'true'
console.log(Number.isSafeInteger(5));
// prints 'false'
console.log(Number.isSafeInteger('19'));
// prints 'false'
console.log(Number.isSafeInteger(Math.pow(2, 53)));
// prints 'true'
console.log(Number.isSafeInteger(Math.pow(2, 53) - 1));
Number.isSafeInteger() is supported in all modern browsers, except Internet Explorer. The polyfill for this method was taken from es6-shim by Paul Miller as:
Number.isSafeInteger = Number.isSafeInteger || function (value) {
return Number.isInteger(value) && Math.abs(value) <= Number.MAX_SAFE_INTEGER;
};
Please note that this polyfill relies on the Number.isInteger() method discussed previously, so you need to do the latter polyfill to use this method.
ECMAScript 6 also introduces two related constant values: Number.MAX_SAFE_INTEGER and Number.MIN_SAFE_INTEGER. The former represents the largest safe integer in JavaScript, which is 2 to the power of 53 - 1, while the latter represents the smallest safe integer, which is - (2 to the power of 53 - 1).
Number.parseInt() and Number.parseFloat()
Number.parseInt() and Number.parseFloat() methods both belong to the same section, because unlike the ones mentioned in this article To other similar methods, they already existed in previous versions of ECMAScript. Therefore, you can use them in the same way as you currently do, and get the same results. The syntax is as follows:
// Signature of Number.parseInt Number.parseInt(string, radix) // Signature of Number.parseFloat Number.parseFloat(string)
where string represents the value to be parsed and radix is the radix string you want to use for conversion.
The following code snippet shows example usage:
// Prints '-3'
console.log(Number.parseInt('-3'));
// Prints '4'
console.log(Number.parseInt('100', 2));
// Prints 'NaN'
console.log(Number.parseInt('test'));
// Prints 'NaN'
console.log(Number.parseInt({}));
// Prints '42.1'
console.log(Number.parseFloat('42.1'));
// Prints 'NaN'
console.log(Number.parseFloat('test'));
// Prints 'NaN'
console.log(Number.parseFloat({}));
Node和所有现代浏览器都支持这些方法，Internet Explorer除外。如果您想要使用它们，您可以简单地调用它们的全局方法，如下所示：
// Polyfill Number.parseInt
Number.parseInt = Number.parseInt || function () {
return window.parseInt.apply(window, arguments);
};
// Polyfill Number.parseFloat
Number.parseFloat = Number.parseFloat || function () {
return window.parseFloat.apply(window, arguments);
};
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