If you are familiar with Python, you will know that slicing in Python greatly simplifies operations. If you look back at the JS slicing family, there are still one or two of them, slice, splice, substr, substring, etc. There are some people who have basic support for the rest of the work.
[: :] operator
JavaScript based syntax, if you write this, then you should try, (; ￢ _ ￢), here we use the way of function to achieve the slice effect.
Go straight to code (array)
if (!Array.prototype.select) {
Object.defineProperty(Array.prototype. 'select'. {
value: function(item) {
'use strict';
if (this = = null) {
throw new TypeError('Array.prototype.select called on null or undefined');
}
if (!Array.isArray(this)) {// This must be an Array type
throw new TypeError('This Object is not Array');
}
var arr = [];
var i = arguments[0] || 0;// Start position
var len = this.length >>> 0;// The length of the array
var end = len;// End position
if (!arguments[1]) {
if (arguments[1] = = = 0) {// Resolve the case where the end position is 0
end = 0;
}
}else{
end = Math.min(Math.abs(arguments[1]), len);
// If the end position is too long, set it to the end position of the array
}
end = end > = 0 ? end : len + end;// End position is negative
var step = arguments[2] || 1;// The default value is consecutive
step = Math.abs(step);
if (arguments[2] < 0) {// Reverse values
for (i = end - 1; i > = 0; i = i - step) {
arr.push(this[i]);
}
}else {
for (i; i < end; i = i + step) {
arr.push(this[i]);
}
}
return arr;
},
configurable: true.
enumerable: false.
writable: true.
});
}
Copy the codeAbout arrays
if (!Array.isArray) {
Object.defineProperty(Array. 'isArray'. {
value: function(arg) {
return Object.prototype.toString.call(arg) = = = '[object Array]';
},
configurable: true.
enumerable: false.
writable: true
});
}
Copy the codeSlicing of strings
if (!String.prototype.select) {
Object.defineProperty(String.prototype. 'select'. {
value: function(item) {
'use strict';
if (this = = null) {
throw new TypeError('String.prototype.select called on null or undefined');
}
if (typeof this ! = = "string") {
throw new TypeError('This Object is not String');
}
var arr = [];
var i = arguments[0] || 0;// Start position
var len = this.length >>> 0;// The length of the array
var end = len;// End position
if (!arguments[1]) {
if (arguments[1] = = = 0) {// Resolve the case where the end position is 0
end = 0;
}
}else{
end = Math.min(Math.abs(arguments[1]), len);
// If the end position is too long, set it to the end position of the array
}
end = end > = 0 ? end : len + end;// End position is negative
var step = arguments[2] || 1;// The default value is consecutive
step = Math.abs(step);
if (arguments[2] < 0) {// Reverse values
for (i = end - 1; i > = 0; i = i - step) {
arr.push(this[i]);
}
}else {
for (i; i < end; i = i + step) {
arr.push(this[i]);
}
}
return arr.join(' ');
},
configurable: true.
enumerable: false.
writable: true.
});
}
Copy the codeTest the
var arr = [1.2.3.4.5.6.7.8.9];
console.log(arr.select(1.-1.2));
console.log(arr.select(1.-1.-2));
Copy the code
Source: slice operation, and some other array operations