I recently worked on a project, which involved the processing of js judgment of data types. I searched for relevant information on the Internet, and personally tested the judgment of various data types. It is absolutely safe. Below, the editor will share with you a summary of the specific content for your reference!
1. Data types in JS
1. Numeric type (Number): including integers and floating point numbers.
2. Boolean
3. String
4. Object
5. Array
6. Null
7. Undefined
2. Determine the data type of a variable
1. Numeric type (number)
The more commonly used judgment method is:
function isNumber(val){ return typeof val === 'number'; }
But in some cases it won’t work, for example:
var a; alert(isNumber(parseInt(a)));
What pops up here is true, as shown in the figure below:
But in fact the variable a is NaN, which cannot be used for numerical operations.
So the above function can be modified as:
function isNumber(val){ return typeof val === 'number' && isFinite(val); }
After modification, false will pop up, as shown in the figure below:
By the way, let me introduce the JavaScript isFinite() function. The isFinite() function is used to check whether its parameter is infinity. If number is a finite number (or can be converted to a finite number), then it returns true. Otherwise, if number is NaN (not a number), or a positive or negative infinity number, false is returned.
2. Boolean
The judgment of Boolean type is relatively simple and can be judged by the following method:
/* 判断变量val是不是布尔类型 */ function isBooleanType(val) { return typeof val ==="boolean"; }
Test code:
Run result:
3. String (String)
The judgment of string type is relatively simple, you can Use the following method to judge:
/* 判断变量是不是字符串类型 */ function isStringType(val) { return typeof val === "string"; }
Test code:
Running results:
4. Undefined
The undefined judgment is relatively simple and can be judged by the following method:
/* 判断变量是不是Undefined */ function isUndefined(val) { return typeof val === "undefined"; }
Test code:
Run Result:
5. Object (Object)
Since typeof will also return object when the variable is Null, Object cannot Use typeof to judge directly.
It should look like this:
function isObj(str){ if(str === null || typeof str === 'undefined'){ return false; } return typeof str === 'object'; }
Test code:
Running result:
6. Null value (Null)
To judge the null value, use val === null to test
function isNull(val){ return val === null; }
Code:
/* 判断变量是不是null */ function isNull(val){ return val === null; } /*测试变量*/ var a; var b = null; var c = "str"; //弹出运行结果 alert("变量a是null的判断结果是:"+isNull(a));//false alert("变量b是null类型的判断结果是:"+isNull(b));//true alert("变量c是null类型的判断结果是:"+isNull(c));//false
Running result:
##7. Array/*判断变量arr是不是数组 方法一 */ function isArray(arr) { return Object.prototype.toString.apply(arr) === '[object Array]'; } /*判断变量arr是不是数组 方法二 */ function isArray(arr) { if(arr === null || typeof arr === 'undefined'){ return false; } return arr.constructor === Array; }
## Test code:
Run results:
The above content is a summary of JavaScript knowledge points introduced by the editor (six): JavaScript determines variable data type Related knowledge, I hope it will be helpful to everyone. If you want to know more, please pay attention to the PHP Chinese website!
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