How to determine whether it is a numeric type in javascript

Method: 1. Use the typeof keyword and isNaN() function to judge; 2. Use the typeof keyword and isFinite() function to judge; 3. Use "Object.prototype.toString.call" to judge; 4. Use regular expressions to determine.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

js summary of judging numeric types

When I was writing code recently, some logic needed to judge the numeric type. When I used it, I realized that the method I understood was not very strict, and then I decided to check it out. Summary of data to understand which methods are more rigorous

The first one: typeof isNaN

Use typeof to determine whether it is a numeric type, but NaN is also a numeric type. In order To eliminate this possibility, further filter out by isNaN. This method will miss Infinity

function isNumber(num) {
	return typeof num === 'number' && !isNaN(num)
}

The second type: typeof isFinite

Use typeof to determine whether it is a numeric type, but NaN and Infinity are also numeric types. In order To eliminate this possibility, further filter out NaN and Infinity through isFinite

function isNumber(num) {
	return typeof num === 'number' && isFinite(num)
}

[Recommended learning: javascript Advanced Tutorial]

The third type: Object. prototype.toString.call

function isNumber(num) {
	return Object.prototype.toString.call(num) === '[object Number]'  && !isNaN(num)
}

Fourth: Regular expression (the most recommended one)

function isNumber(num) {
	return /^[0-9]+.?[0-9]*$/.test(num)
}

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