In JavaScript, why should you use local variables whenever possible? _javascript skills
If you don’t do this, how much loss will it cause to performance? This article will explore the answers to these questions and fundamentally understand what factors are related to the reading and writing performance of variables. Copyright Statement This article was translated from Nicholas C. Zakas on personal website< on February 10, 2009 "Javascript Variable Performance” published on /FONT>. Original text is the only official version. This article is a Simplified Chinese Translation authorized by the original author (Nicholas C. Zakas). The translator (明达) has made a lot of efforts to ensure the accuracy of the translation, and promises that the content of the translation is completely faithful to the original text, but it may still contain omissions and inaccuracies. Welcome everyone Correction. The content of the translation notes is informal and represents only the translator’s personal views. The following is a translation of the original text: On the issue of how to improve the performance of Javascript, the most commonly heard suggestion is to use local variables instead of global variables. This advice has always stuck with me and never been questioned in my nine years of working in web development, and the basis for this advice comes…
In JavaScript, why should you use local variables whenever possible?
If you don’t do this, how much loss will it cause to performance? This article will explore the answers to these questions and fundamentally understand what factors are related to the reading and writing performance of variables. Copyright Statement This article was translated from Nicholas C. Zakas on personal website< on February 10, 2009 "Javascript Variable Performance” published on /FONT>. Original text is the only official version. This article is a Simplified Chinese Translation authorized by the original author (Nicholas C. Zakas). The translator (明达) has made a lot of efforts to ensure the accuracy of the translation, and promises that the content of the translation is completely faithful to the original text, but it may still contain omissions and inaccuracies. Welcome everyone Correction. The content of the translation notes is informal and represents only the translator’s personal views. The following is a translation of the original text: On the issue of how to improve the performance of Javascript, the most commonly heard suggestion is to use local variables instead of global variables. This advice has always stuck with me and never been questioned in my nine years of working in web development, and the basis for this advice comes…
In JavaScript, why null==0 is false and null greater than=0 is true (personal research)_javascript skills-js tutorial
In life, we are constantly writing code and writing Javascript, and we rarely have time to conduct conceptual research. As for me, I have nothing to do today, so I studied the relationship between “null” and “0”. I hope everyone can gain something from reading it. The code is as follows: alert( null>=0) The code is as follows: What will pop up in the above code? False? True? Actually it is true. So why? Why is “null>=0” true? When null>=0, it is forced to a numeric type. When comparing null>=0, it is the answer obtained by comparing null<0. If a=b is false, if a=b is true, that is, 0<0 is false, that is, null0 is true. So null>=0 is true. The code is as follows: alert(null==0) What will pop up in the above code? False? True? In fact, it is false. “null==0” is treated specially and will not be converted to a numeric type or a numerical value. However, if the left side is a string and the right side is a numerical value, it will be converted. “null” is an object (empty object, without any properties and methods). And “0” is a number. As mentioned before, “==” does not…
In JavaScript, when an associative array a is assigned to b, and then the content of a is changed, why does b also change?
JS: var a = {“Client”:”jQuery”,”Server”:”PHP”}; var b = a; a[“New”] = “Element”; console.log(b); // Output Object { Client=”jQuery”, Server=”PHP”, New=”Element”} PHP routine 1: $a = array(‘Client’=>’jQuery’,’Server’=>’PHP’); $b = $a; $a[‘New’] = ‘Element’; var_export($b); //Output array(‘Client’=>’jQuery’,’Server’=>’PHP’) PHP routine 2: $a = array(‘Client’=>’jQuery’,’Server’=>’PHP’); $b = &$a; //Reference assignment $a[‘New’] = ‘Element’; var_export($b); //Output array(‘Client’=>’jQuery’,’Server’=>’PHP’,’New’=>’Element’) In Javascript, when an associative array a is assigned to b, and then the content of a is changed, why does b also change? Reply content: JS: var a = {“Client”:”jQuery”,”Server”:”PHP”}; var b = a; a[“New”] = “Element”; console.log(b); // Output Object { Client=”jQuery”, Server=”PHP”, New=”Element”} PHP routine 1: $a = array(‘Client’=>’jQuery’,’Server’=>’PHP’); $b = $a; $a[‘New’] = ‘Element’; var_export($b); //Output array(‘Client’=>’jQuery’,’Server’=>’PHP’) PHP routine 2: $a = array(‘Client’=>’jQuery’,’Server’=>’PHP’); $b = &$a; //Reference assignment $a[‘New’] = ‘Element’; var_export($b); //Output array(‘Client’=>’jQuery’,’Server’=>’PHP’,’New’=>’Element’) In Javascript, when an associative array a is assigned to b, and then the content of a is changed, why does b also change? For non-ordinary types such as arrays (strings, integers, Boolean), your assignment is equivalent to address copying, that is, a and b occupy the same address. So if b is changed, a will also change. Essentially, a and b are the same thing. This answer here is…
In JavaScript, are these two arrays the same? -php tutorial
var arr1 =new Array(“Luffy”,”Zoro”,”Sanji”); var arr2 =new Array(“Cocoro”,”Qimonni”,”Kumbei”,”Iceberg”); var arr3 =new Array(“Kunis”,”Ganfulu”,”Weibo”,”Laki”); var arrAll1 = new Array(arr1,arr2,arr3); console.log( arrAll1.toString() ); arrAll2=new Array().concat(arr1,arr2,arr3) console.log( arrAll2.toString() ); Are arrAll1 and arrAll2 here the same array?? Anyway, it’s not a thing in PHP, but I don’t know if it is a thing here; But using tostring here looks the same; Reply content: var arr1 =new Array(“Luffy”,”Zoro”,”Sanji”); var arr2 =new Array(“Cocoro”,”Qimonni”,”Kumbei”,”Iceberg”); var arr3 =new Array(“Kunis”,”Ganfulu”,”Weibo”,”Laki”); var arrAll1 = new Array(arr1,arr2,arr3); console.log( arrAll1.toString() ); arrAll2=new Array().concat(arr1,arr2,arr3) console.log( arrAll2.toString() ); Are arrAll1 and arrAll2 here the same array?? Anyway, it’s not a thing in PHP, but I don’t know if it is a thing here; But using tostring here looks the same; Obviously different. arrAll1 is a two-dimensional array, arrAll2 is a one-dimensional array You will know when you visit: arrAll1[0][0]; // “Luffy” arrAll2[0]; // “Luffy” The answers are the same, but you will find that they have some differences, as follows: arrAll1.length; //The result is 3 arrAll2.length; //The result is 11 This is the difference, the first one just puts the three arrays together,while the second one does take out each element of the three arrays separately and puts them into arrAll2
In javascript, how to delete duplicate elements in a two-dimensional array_javascript tips
I’ve been trying for a long time, but I still haven’t come up with a solution. Please give me some ideas. [Ctrl+A to select all Note: If you need to introduce external Js, you need to refresh to execute]
In JavaScript, are these two arrays the same?
var arr1 =new Array(“Luffy”,”Zoro”,”Sanji”); var arr2 =new Array(“Cocoro”,”Qimonni”,”Kumbei”,”Iceberg”); var arr3 =new Array(“Kunis”,”Ganfulu”,”Weibo”,”Laki”); var arrAll1 = new Array(arr1,arr2,arr3); console.log( arrAll1.toString() ); arrAll2=new Array().concat(arr1,arr2,arr3) console.log( arrAll2.toString() ); Are arrAll1 and arrAll2 here the same array?? Anyway, it’s not a thing in PHP, but I don’t know if it is a thing here; But using tostring here looks the same; Reply content: var arr1 =new Array(“Luffy”,”Zoro”,”Sanji”); var arr2 =new Array(“Cocoro”,”Qimonni”,”Kumbei”,”Iceberg”); var arr3 =new Array(“Kunis”,”Ganfulu”,”Weibo”,”Laki”); var arrAll1 = new Array(arr1,arr2,arr3); console.log( arrAll1.toString() ); arrAll2=new Array().concat(arr1,arr2,arr3) console.log( arrAll2.toString() ); Are arrAll1 and arrAll2 here the same array?? Anyway, it’s not a thing in PHP, but I don’t know if it is a thing here; But using tostring here looks the same; Obviously different. arrAll1 is a two-dimensional array, arrAll2 is a one-dimensional array You will know when you visit: arrAll1[0][0]; // “Luffy” arrAll2[0]; // “Luffy” The answers are the same, but you will find that they have some differences, as follows: arrAll1.length; //The result is 3 arrAll2.length; //The result is 11 This is the difference, the first one just puts the three arrays together,while the second one does take out each element of the three arrays separately and puts them into arrAll2
In JavaScript, why should you use local variables whenever possible? _javascript skills
If you don’t do this, how much loss will it cause to performance? This article will explore the answers to these questions and fundamentally understand what factors are related to the reading and writing performance of variables. Copyright Statement This article was translated from Nicholas C. Zakas on personal website< on February 10, 2009 "Javascript Variable Performance” published on /FONT>. Original text is the only official version. This article is a Simplified Chinese Translation authorized by the original author (Nicholas C. Zakas). The translator (明达) has made a lot of efforts to ensure the accuracy of the translation, and promises that the content of the translation is completely faithful to the original text, but it may still contain omissions and inaccuracies. Welcome everyone Correction. The content of the translation notes is informal and represents only the translator’s personal views. The following is a translation of the original text: On the issue of how to improve the performance of Javascript, the most commonly heard suggestion is to use local variables instead of global variables. This advice has always stuck with me and never been questioned in my nine years of working in web development, and the basis for this advice comes…
In javascript, what type is NaN?
The NaN attribute represents a value that is “not a number”. This special value occurs because the operation cannot be performed, either because one of its operands is non-numeric (e.g., “abc” / 4) or because the result of the operation is non-numeric (e.g., the divisor is zero). (Recommended tutorial: js tutorial) First of all, although NaN means “not a number”, its type is Number. console.log(typeof NaN === “number”); // logs “true” In addition, NaN and any Comparing things – even itself, the result is false: console.log(NaN === NaN); // logs “false” If you want to test whether a number is equal to NaN, you can use value !== value. Will only produce true if the value is equal to NaN. In addition, ES6 provides a new Number.isNaN() function, which is a different function and more reliable than the old global isNaN() function. The above is what type of NaN is in Javascript? For more details, please pay attention to other related articles on 1024programmer.com!
In JavaScript, null>=0 is true, but null==0 is false. Detailed explanation of the value of null
In Javascript, null>=0 is true, but null==0 is false. Detailed explanation of the value of null 1.Foreword Today I saw friends discussing a question, asking whether null is equal to 0. After hearing this, I quickly wrote a demo and tried it myself. What’s going on? Why are the two judgments of console.log(null = 0); true? 2. Check information If we want to know exactly what this problem is about, then we need to review our ECMAScript Language Specification (HTML version), which translates to ECMAScript Language Specification (HTML version). 2.1 Internal equality operation algorithm First, let’s take a look at ES3’s algorithm implementation of internal equality operations. 11.9.3 The Abstract Equality Comparison Algorithm The comparison x == y, where x and y are values, produces true or false. Such a comparison is performed as follows: 1. If Type(x) is different from Type(y), Go to step 14. 2. If Type(x) is Undefined, return true. 3. If Type(x) is Null, return true. 4. If Type(x) is not Number, go to step 11. 5. If x is NaN, return false. 6. If y is NaN, return false. 7. If x is the same number value as y, return true. 8. If x is…
